Prep: Preheat your oven to 350°F. Grease a 9x13-inch baking pan with butter or cooking spray, then line the bottom with parchment paper. This prevents sticking and makes removal easier. (5 minutes)

Dry ingredients: In a small bowl, whisk together 2 cups all-purpose flour, 1 teaspoon baking powder, and 1/2 teaspoon salt. Set this bowl aside. (2 minutes) Checkpoint: You should see a light, even mixture with no lumps.

Cream butter and sugar: In a large mixing bowl, combine 1/2 cup softened unsalted butter and 1 cup granulated sugar. Use an electric mixer on medium speed and beat for 2-3 minutes until the mixture looks light, fluffy, and pale yellow. (3 minutes) Checkpoint: The mixture should triple in volume and look like fluffy clouds.

Add eggs: Add 2 large eggs one at a time to the butter mixture, beating well for 30 seconds after each egg is added. This incorporates air and helps the cake rise. (2 minutes) Checkpoint: After beating, the mixture should look smooth and creamy with no visible streaks of egg.

Add flavorings: Stir in 2 tablespoons lemon zest and 1 teaspoon vanilla extract with a spatula or wooden spoon for 30 seconds. (1 minute) Checkpoint: You should see tiny flecks of lemon zest throughout.

Alternate wet and dry: Add the flour mixture in 3 portions, alternating with 1/2 cup sour cream (2 portions flour, then sour cream, then remaining flour). After each addition, stir gently with a spatula for 20-30 seconds until just combined. Do not overmix or the cake will become tough. (3 minutes) Checkpoint: The batter should look smooth and creamy with no white streaks of flour visible.

Add lemon juice: Stir in 1/4 cup fresh lemon juice gently with a spatula for just 15 seconds until combined. Do not overmix. (1 minute) Checkpoint: The batter should be smooth and bright yellow.

Fold in raspberries: Gently fold 1 1/2 cups fresh raspberries into the batter using a spatula, using 8-10 slow, careful strokes. Do not stir vigorously or the berries will break apart and color the batter unevenly. (1 minute) Checkpoint: You should see whole raspberries distributed throughout the batter.

Pour into pan: Transfer the batter into your prepared 9x13-inch baking pan. Use a spatula to smooth the top so it's even. (2 minutes)

Make crumb topping: In a small bowl, combine 1/2 cup granulated sugar and 2 tablespoons all-purpose flour. Cut 1/4 cup cold unsalted butter into small cubes (about 1/2-inch pieces) and add to the sugar-flour mixture. Using your fingertips or a pastry cutter, rub the cold butter into the sugar and flour, working quickly so the butter stays cold. You want pea-sized crumbs throughout, not a fine powder. (3 minutes) Checkpoint: The topping should look like coarse breadcrumbs with visible butter pieces throughout.

Add topping: Sprinkle the crumb mixture evenly over the cake batter, covering all the cake. Don't press it down. (1 minute)

Bake: Place the pan in the center of your preheated 350°F oven for 35-40 minutes. The cake is done when the top is golden brown and a toothpick or knife inserted into the center comes out with only moist crumbs (not wet batter). The edges should look set and slightly shrunk away from the pan sides. (40 minutes) Checkpoint: The top should be golden brown, and the toothpick should come out clean or with just a few wet crumbs clinging to it.

Cool in pan: Remove the pan from the oven using an oven mitt and set it on a countertop heat-safe surface. Let the cake cool in the pan for 15 minutes without moving it. During this time, residual heat continues to set the crumb and prevents the cake from breaking apart. (15 minutes)

Transfer to rack: Place a wire cooling rack on top of the baking pan and carefully flip the pan and rack together so the cake falls onto the rack. Gently remove the pan and parchment paper. Let the cake cool completely to room temperature on the rack, about 45 minutes. The cake must be completely cool before adding toppings. (45 minutes) Checkpoint: The cake should feel cool to the touch and not warm at all.

Make whipped cream: About 15 minutes before serving, place a metal mixing bowl and beaters in your freezer to chill them for 10 minutes. Pour 2 cups heavy whipping cream into the chilled bowl. Using an electric mixer on medium-high speed, beat for 1-2 minutes until soft peaks form (the cream will hold its shape for a moment but tips will curl over). (2 minutes) Checkpoint: When you lift the beater, the cream should form a peak that gently folds back on itself.

Sweeten whipped cream: Add 3 tablespoons powdered sugar and 1 tablespoon fresh lemon juice to the whipped cream. Beat for 30-60 seconds more until stiff peaks form (the cream will hold a sharp peak that stands upright). Be careful not to overbeat or you'll make butter. (1 minute) Checkpoint: Lift the beater — the cream should form a sharp peak that stands straight up without folding.

Cut and serve: Using a sharp knife dipped in hot water (wipe between cuts), cut the cooled cake into squares. Transfer each square to a serving plate. Top each piece with a dollop of lemon whipped cream and garnish with 3-4 fresh raspberries and a light sprinkle of fresh lemon zest. Serve immediately. (5 minutes)