Preheat the oven to 350°F (175°C). Grease three 8-inch round cake pans and line the bottoms with parchment paper. Lightly flour the sides.

In a medium bowl, whisk together cake flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy (about 3–5 minutes). Add the eggs one at a time, mixing well after each. Stir in the vanilla extract.

Add the flour mixture to the butter mixture in three additions, alternating with the sour cream. Begin and end with the dry ingredients. Mix until just combined—do not over mix. Fold in the toasted chopped pecans.

Divide the batter evenly between the prepared pans. Bake for 30–35 minutes or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.

In a medium saucepan, melt the butter over medium heat. Add the brown sugar and stir constantly until it dissolves and begins to bubble (about 2–3 minutes). Remove from heat and stir in the sweetened condensed milk. Let the mixture cool slightly, then beat in sifted powdered sugar and vanilla extract until smooth and spreadable.

Place one cake layer on a serving plate. Spread a generous amount of caramel frosting on top. Repeat with the second and third layers, then frost the top and sides of the entire cake.

Press additional toasted pecans around the sides and sprinkle on top for garnish. Let the cake set for 30 minutes before slicing. Serve at room temperature for best flavor.