Prep the pan: Preheat your oven to 375°F (190°C). Spray a large loaf pan (about 9×5 inches) with nonstick cooking spray on all sides, including the bottom. Set aside. Checkpoint: Your oven is preheated and your pan is ready to use.

Cream butter and sugars: In a large mixing bowl, add 5 tablespoons softened butter, 1/2 cup granulated sugar, and 2 tablespoons brown sugar. Using an electric mixer on medium speed, beat for 2–3 minutes until the mixture is light, fluffy, and pale in color. You should see it increase slightly in volume. Checkpoint: The mixture looks light and creamy, not dense.

Add bananas and eggs: Add 1 1/3 cups mashed ripe bananas (about 3–4 very ripe bananas, mashed with a fork until mostly smooth with tiny lumps okay), 1 whole egg, and 2 egg whites to the butter mixture. Beat on medium speed for 1–2 minutes until everything is well combined and the mixture looks uniform. Checkpoint: You see no streaks of banana or egg white—everything is blended together.

Prepare dry ingredients: In a medium bowl, sift together 2 1/2 cups all-purpose flour, 1 teaspoon baking soda, and 1/2 teaspoon salt using a whisk or sifter. Sifting removes lumps and adds air. Checkpoint: Your dry mixture looks light and fluffy with no clumps.

Combine wet and dry: Add the sifted dry ingredients to the banana mixture. Using a rubber spatula or wooden spoon, stir gently by hand until just combined—do not overmix. It's okay if a few flour streaks remain; overmixing can make the bread dense. The batter should look chunky and thick. Checkpoint: No visible dry flour remains, but you haven't stirred for more than 30 seconds.

Add walnuts: Fold in 1/3 cup chopped walnuts with 3–4 gentle strokes of your spatula until evenly distributed. Checkpoint: Walnuts are scattered throughout the batter.

Pour into pan: Pour the batter into your prepared loaf pan and smooth the top with a spatula so it's level. Checkpoint: Batter fills the pan about 2/3 full with a smooth, even surface.

Bake: Place the loaf pan on the middle rack of your preheated 375°F oven. Bake for 50–60 minutes. At 50 minutes, insert a wooden toothpick or wooden pick into the center of the loaf (avoid hitting a walnut). The pick should come out clean or with just a tiny crumb or two—no wet batter. The top should be golden brown. If the top is browning too fast, tent loosely with aluminum foil for the last 10–15 minutes. Checkpoint: A wooden pick inserted in the center comes out clean or with only a few dry crumbs, and the top is golden brown.

Cool in pan: Remove the loaf pan from the oven and let it sit on a countertop for 5 minutes without moving it. Checkpoint: The bread has pulled slightly away from the pan edges.

Remove from pan: Run a thin butter knife around all four inside edges of the pan to loosen the bread. Place a wire cooling rack upside down over the top of the pan, then flip the pan and rack together so the bread slides out onto the rack. It should come out easily. If it sticks, let it cool another 2–3 minutes and try again. Checkpoint: The bread is fully released from the pan and resting on the cooling rack.

Cool: Let the banana nut bread cool on the wire rack for at least 10 minutes before slicing. For easier, cleaner slices, cool completely (about 2 hours) before cutting. If serving warm, wait at least 10 minutes so it's stable enough to slice. Checkpoint: The bread is cool enough to handle and slice cleanly.