Step 1

For the cake: Preheat the oven to 350 degrees F. Spray three 8-inch round cake pans with cooking spray.

Step 2

Place the brown sugar, granulated sugar and butter in a large bowl; beat with a mixer at medium speed until well blended, 3 to 5 minutes.

Step 3

Turn the mixer to low and add the eggs, 1 at a time, beating well after each addition. Beat in the pumpkin and vanilla.

Step 4

Combine the flour, cinnamon, baking powder, baking soda and salt in a bowl, stirring well with a whisk.

Step 5

Add the flour mixture and buttermilk alternately to the sugar mixture, beginning and ending with the flour mixture. Spoon the batter into the prepared pans.

Step 6

Bake until a wooden pick inserted in the centers comes out clean, 22 to 25 minutes. Cool in the pans on a wire rack for 10 minutes, then remove from the pans and cool completely on the wire rack, about 1 hour.

Step 7

For the cinnamon buttercream: In a large bowl or stand mixer fitted with the whisk attachment, whip the butter on medium-high speed until pale and creamy, 3 to 5 minutes. With the mixer on a slow speed, carefully add the confectioners' sugar 1 cup at a time until combined, followed by the vanilla and cinnamon. Add the heavy cream a little at a time. (If you need a thicker frosting, add more confectioners' sugar; if you need a thinner consistency, add in more heavy cream.)

Step 8

Place a cooled cake layer on a cake stand. (This recipe should yield very level cake layers, but if your layers are domed, level them before assembling.) Cover with about 1/2 cup buttercream. Scatter 1/3 cup of chopped pecan over the top.

Step 9

Repeat with the next layer of cake, covering with 1/2 cup buttercream and 1/3 cup chopped pecans. Place the final layer of cake on top.

Step 10

Place the remaining buttercream in a pastry bag fitted with a large open star tip (such as #362). Pipe out a design on the top of the cake (the sides will be left "naked").

Step 11

Sprinkle the remaining pecans over the top, then drizzle the cake with caramel sauce. Serve immediately.