Preheat oven to 350°F (175°C). Spread pecans on a baking sheet and toast 6–8 minutes until fragrant. Let cool, then chop coarsely.

Reduce oven to 325°F (163°C). Grease and flour three 8-inch round pans (or two 9-inch pans for a two-layer cake) and line the bottoms with parchment.

Whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg.

In a stand mixer, cream butter with both sugars until pale and airy, about 3–4 minutes.

Add eggs one at a time, mixing well after each, then stir in vanilla.

Fold in mashed bananas.

Alternate folding the dry ingredients and buttermilk into the butter mixture in three additions, beginning and ending with the dry ingredients. Fold in toasted pecans gently.

Divide batter evenly among prepared pans. Smooth tops and bake 22–28 minutes (for 8-inch pans) until a toothpick comes out with a few moist crumbs and the tops spring back.

Let layers cool in pans for 10 minutes, then invert onto wire racks to cool completely.

In a medium heavy-bottomed saucepan, melt the granulated sugar over medium heat, stirring constantly until it liquefies and turns a deep amber.

Immediately stir in butter (careful — it will sizzle). Pour in warmed cream slowly while stirring; the mixture will bubble vigorously. Stir until smooth.

Remove from heat, stir in salt, and let cool until warm but pourable. Reserve 1/2 cup for the buttercream and a few spoonfuls for brushing between layers.

Beat butter until smooth. Gradually add powdered sugar until incorporated.

Beat in reserved cooled caramel and a pinch of salt. Add heavy cream 1 tbsp at a time to reach a silky, spreadable consistency.

If needed, level cake layers with a serrated knife.

Place the first layer on a cake board; brush lightly with warmed caramel. Spread a thin layer of buttercream, sprinkle a scattering of chopped pecans and optional banana slices.

Repeat with the second layer. For a three-layer cake, finish with the third layer brushed with caramel (do not over-soak).

Crumb-coat with a thin layer of buttercream and chill for 20–30 minutes.

Apply a smooth final coat of buttercream. Drizzle remaining warm caramel over the top, letting it pool and trickle down the sides, and garnish with toasted pecans.