Banana Cake with Buttercream Frosting

Ingredients (with roles explained)

This recipe is formatted for a 9×13-inch pan.

For the Cake

1 ¼ cups granulated sugar
— Sweetness, helps with browning and tender crumb by interacting with fat and eggs.
1 cup sour cream
— Adds moisture, richness, and a gentle tang; its acidity also tenderizes the gluten for a soft crumb.
2 large eggs
— Structure, lift and emulsification; eggs bind the batter and trap air as the cake bakes.
½ cup (1 stick) unsalted butter, melted
— Fat for flavor and moistness; melted butter blends easily into this batter for a tender texture.
1 ½ cups mashed ripe bananas (about 3 medium bananas)
— The star flavor and natural sweetness; bananas contribute moisture and density so the cake remains tender.
2 cups cake flour
— Lower protein than all-purpose flour; yields a lighter, finer crumb. (If using all-purpose, see tips below.)
1 teaspoon baking soda
— Primary leavening here; reacts with the sour cream and banana to produce lift and a soft texture.
½ teaspoon fine sea salt
— Balances sweetness and enhances the cake’s flavor profile.
1 teaspoon vanilla extract
— Aroma and depth; brightens the banana flavor.

For the Buttercream Frosting

4 tablespoons (¼ cup) salted butter, softened
— Provides richness and flavor; use salted to balance the intense sweetness of the powdered sugar.
½ cup heavy cream
— Adds creaminess and helps achieve a spreadable, silky texture.
1 teaspoon vanilla extract
— Rounds out the frosting’s flavor.
2 ½ cups confectioners’ (powdered) sugar, sifted
— Sweetness and structure for the frosting; sift to avoid lumps and ensure a smooth finish.
Optional: 2–4 tablespoons high-ratio shortening (see note)
— Substituting part of the butter with a high-ratio shortening stabilizes frosting for warmer climates or longer decor life; this echoes the old Crisco-based frostings.

Step-by-Step Instructions — Easy & Reliable

Preheat & prep: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking pan and line it with parchment if you prefer easy removal.
Combine wet ingredients: In a medium bowl, whisk together 1¼ cups sugar, 1 cup sour cream, 2 large eggs, and ½ cup melted butter until homogeneous and slightly glossy. Stir in 1½ cups mashed ripe bananas and 1 teaspoon vanilla extract.
Mix dry ingredients: In a separate bowl, whisk together 2 cups cake flour, 1 teaspoon baking soda, and ½ teaspoon salt until evenly combined.
Fold together: Add the dry ingredients to the wet mixture in two additions, stirring gently after each addition until just incorporated. Avoid overmixing — a few streaks of flour are fine. Overmixing develops gluten and can make the cake dense.
Bake: Pour the batter into the prepared 9×13 pan and smooth the top. Bake at 375°F for 25–35 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs attached. Oven times vary — start checking at 22 minutes.
Cool: Remove the cake from the oven and let it cool in the pan on a wire rack for 20 minutes. Run a thin knife around the edges, then invert or leave in pan and cool completely before frosting. Frosting a warm cake causes the buttercream to melt and slide.
Make the buttercream: In a large bowl, beat 4 tablespoons softened butter (and optional 2–4 tablespoons high-ratio shortening) until creamy. Gradually add 2½ cups sifted confectioners’ sugar, alternating with ½ cup heavy cream, beating to spreadable consistency. Add 1 teaspoon vanilla and a pinch of salt if desired. If frosting is too soft, chill 10 minutes and rewhip; if too stiff, add 1 tablespoon cream at a time.
Frost the cake: Once the cake is completely cool, use an offset spatula to spread the buttercream evenly. For a classic look, create gentle swirls with the spatula. If you like, reserve a small amount of frosting to pipe a border.

Why This Recipe Works

This cake balances moisture and lift by combining acidic sour cream with baking soda, which creates an airy yet tender crumb. The high banana ratio keeps the cake moist for days, while melted butter and eggs add richness and structure. Using cake flour produces a finer, softer texture — but the recipe is forgiving if you need to use all-purpose (see conversion tips).

Pro Tips for Perfect Results

Bananas: Use fully ripe bananas with brown spots — they are sweeter and pack more flavor. Mash thoroughly for an even crumb.
Flour swap: If you only have all-purpose flour, make a lighter cake by replacing 2 cups AP with 2 cups minus 4 tablespoons AP + 4 tablespoons cornstarch (to mimic cake flour). Sift for best texture.
Room temperature eggs & sour cream: Ingredients at room temperature emulsify better, giving a smoother batter and more even rise.
Don’t overbake: Pull the cake when a toothpick shows a few moist crumbs — residual heat finishes the bake and prevents dryness.
Stability in warm climates: Substitute 2–3 tablespoons of butter with high-ratio shortening if you need the frosting to hold up in heat (echoes the old Crisco method).
Make ahead: The unfrosted cake keeps well in an airtight container at room temperature for 1 day or refrigerated for 3 days. Frost before serving.

Serving Suggestions

Slice and serve slightly chilled or at room temperature with a scoop of vanilla ice cream for an indulgent dessert.
Top with toasted chopped walnuts or pecans for crunch and visual contrast.
For brunch, pair slices with strong coffee or a milky chai — the cake’s tang from sour cream plays beautifully with bold beverages.
Garnish with thin banana slices just before serving (they brown quickly) or lightly caramelize slices with a torch for a showy finish.

Variations & Notes

Spiced Banana Cake: Add ½ teaspoon cinnamon and a pinch of nutmeg to the dry ingredients.
Banana-Cream Cheese Frosting: Replace half the butter in the frosting with 4 oz cream cheese (softened) for tang and richness.
Sheet Cake or Cupcakes: This batter adapts well — bake cupcakes at 350°F for 18–22 minutes.