Preheat your oven to 350°F (175°C). Grease two 20 cm round cake pans and line the bottoms with parchment paper.

In a bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt.

In another large bowl, cream the softened butter and granulated sugar until the mixture is light and fluffy. Add the eggs one at a time, followed by the vanilla extract, and mix well.

Gradually add the dry ingredients and buttermilk to the butter mixture, alternating between them and mixing on low speed. Slowly pour in the warm water until the batter is smooth.

Divide the batter evenly between the two prepared pans.

Bake for 30-35 minutes, or until a toothpick comes out clean.

Let the cakes cool in the pans for about 10 minutes, then transfer them to a wire rack to cool completely.

Melt the butter and brown sugar in a saucepan over medium heat. Stir in the heavy cream and let it simmer gently for about 2 minutes. Remove from heat and allow it to cool for a few minutes.

Stir in the powdered sugar, vanilla extract, and chopped pecans, mixing until smooth and spreadable.

Place the first layer of cake on a serving plate. Spread a generous layer of caramel pecan cream on top, then place the second cake layer on top. Cover the entire cake with the remaining cream.

For an extra touch, decorate with additional pecan pieces or chocolate shavings.