Preheat and prepare pan: Preheat oven to 350°F. Line the bottom of a 9-inch springform pan with parchment paper and lightly grease the sides. Set aside. Checkpoint: You are ready to move on when the pan is prepared and the oven has reached 350°F.

Make cookie crust: Crush 12 lemon wafer cookies into fine crumbs (you should have about 1 cup). Mix 2 tablespoons melted butter with the crumbs until they resemble wet sand. Press the mixture firmly and evenly across the bottom of the prepared pan, creating a compact layer about 1/4-inch thick. Bake for 5 minutes until the crust is lightly set and dry to the touch. Remove from oven and let cool completely on a wire rack, about 10 minutes. Checkpoint: You are ready to move on when the crust is completely cool and firm to the touch.

Combine dry ingredients for cake: In a small mixing bowl, whisk together 2 cups all-purpose flour, 1 teaspoon baking powder, and 1/2 teaspoon salt until no lumps remain. Set this bowl aside. Checkpoint: You are ready to move on when the dry ingredients are fully combined.

Cream butter and sugar: In a large mixing bowl, beat 1/2 cup softened unsalted butter and 1 cup granulated sugar together using an electric mixer on medium-high speed for 3–4 minutes. The mixture should look pale, fluffy, and creamy like frosting. Scrape down the bowl sides with a spatula. Checkpoint: You are ready to move on when the butter-sugar mixture is light and fluffy and falls in ribbons from the beaters.

Add eggs one at a time: With the mixer still on medium speed, crack 1 large egg into the butter-sugar mixture and beat for about 45 seconds. Repeat with the remaining 2 eggs, beating after each addition for 45 seconds. The batter should look slightly curdled or separated—this is normal. Checkpoint: You are ready to move on when all three eggs have been fully incorporated.

Prepare wet ingredients: In a small bowl or measuring cup, combine 1/2 cup whole milk, 1/4 cup fresh lemon juice, 2 tablespoons fresh lemon zest, and 1 teaspoon vanilla extract. Stir gently to combine. Checkpoint: You are ready to move on when the wet ingredients are mixed and you can see the lemon zest distributed throughout.

Alternate wet and dry ingredients: Reduce mixer speed to medium-low. Add 1/3 of the dry flour mixture to the butter-egg mixture and beat for about 30 seconds. Pour in 1/2 of the wet milk mixture and beat for about 30 seconds. Add another 1/3 of the dry mixture, beat for 30 seconds, add the remaining milk mixture, beat for 30 seconds, then add the final 1/3 of dry mixture and beat until just combined (about 30 seconds). Do not overmix. The batter should be smooth and light yellow with visible lemon zest specks. Checkpoint: You are ready to move on when the batter is smooth and no streaks of flour remain.

Pour batter over crust: Carefully pour the lemon batter evenly over the cooled cookie crust layer in the springform pan. Use a spatula or the back of a spoon to smooth the top into an even layer, but do not press down hard. Checkpoint: You are ready to move on when the batter is spread evenly across the crust and about 1/2 inch thick.

Bake the cake layer: Place the pan in the preheated 350°F oven on the middle rack. Bake for 18–22 minutes. The cake is done when a toothpick inserted in the center comes out clean or with just a few moist crumbs, and the top is light golden brown and springs back when lightly touched with your finger. The cake will still jiggle slightly if you gently shake the pan—this is fine. Checkpoint: You are ready to move on when the toothpick test shows the cake is set and the top is golden.

Cool cake completely: Remove the pan from the oven and place it on a wire cooling rack. Let the cake cool at room temperature for at least 30 minutes, until it is completely cool to the touch. You can also refrigerate it for 15 minutes to speed this up. Do not skip this step—the cake must be completely cold before adding the whipped cream filling, or it will melt. Checkpoint: You are ready to move on when the cake is completely cool and no longer warm to the touch.

Chill the mixing bowl and beaters: While the cake cools, place a large metal mixing bowl and the electric mixer beaters in the freezer for 10 minutes. This helps the cream whip faster and hold its shape better. Checkpoint: You are ready to move on when the bowl and beaters are cold to the touch.

Combine whipped cream ingredients: Pour 1 1/2 cups cold heavy whipping cream into the chilled bowl. Add 1/3 cup powdered sugar, 2 tablespoons softened cream cheese, 1 tablespoon fresh lemon juice, and 1 teaspoon lemon zest. Checkpoint: You are ready to move on when all ingredients are in the cold bowl.

Whip the filling: Using the chilled beaters, start mixing on medium speed. Beat for 2–3 minutes until the cream begins to thicken and double in volume. Increase speed to medium-high and continue beating for another 1–2 minutes until stiff peaks form. You will know it's done when you lift the beaters and the cream holds a firm, pointy peak that doesn't fall over. Do not overbeat or the cream will turn into butter. Checkpoint: You are ready to move on when stiff peaks form and the filling holds its shape.

Spread filling over cake: Using a spatula or knife, spread the lemon whipped cream filling evenly over the cooled cake layer, covering it completely with an even 1/2-inch layer. You can also pipe decorative swirls with a piping bag if desired. Checkpoint: You are ready to move on when the filling is evenly spread and covers the entire cake surface.

Initial chill (6+ hours): Cover the springform pan loosely with plastic wrap, being careful not to let it touch the whipped cream. Place in the refrigerator for at least 6 hours, or preferably overnight (up to 24 hours). The cake develops better flavor and the layers firm up as it chills. Do not skip this step. Checkpoint: You are ready to move on when the cake has chilled for at least 6 hours and feels very cold and firm when you press gently on the top.

Prepare garnishes and serve: About 15 minutes before serving, remove the cake from the refrigerator. Slice 2–3 fresh lemons into thin rounds or wedges. If using candied lemon peel, have it ready. Run a thin, warm knife around the inside edge of the springform pan to loosen the cake, then carefully release and remove the springform ring. Checkpoint: You are ready to move on when the springform is removed.

Garnish and cut: Arrange fresh lemon slices and candied lemon peel on top of the cake in a decorative pattern. Using a sharp knife dipped in hot water and wiped dry between cuts, slice the cake into 6–8 wedges. Serve immediately, or return to refrigerator if not serving right away. The cake will keep chilled for up to 3 days. Checkpoint: You are ready to move on when the cake is garnished, sliced, and plated.