Preheat oven to 350-degrees. Coat bottoms of two 8-inch round cake pans with cooking spray; line with wax paper. Coat paper with spray; dust with flour.
Combine boiling water and cocoa in a small bowl; whisk until well blended. Cool
Combine sugar, butter, and vanilla, beat with a mixer on medium speed until well blended. Add eggs one at a time, beating well after each.
Combine flour, baking soda, baking powder and salt. Add flour mixture and cocoa mixture alternately to sugar. Pour into pans. Bake 25 minutes, or until wooden pick inserted in the center comes out clean. Cool in pans on a wire rack 10 minutes. Remove from pans and cool completely.
To prepare frosting, melt butter in a small saucepan; add brown sugar and 2 TBSP. milk. Cook until sugar melts. Remove from heat and cool slightly. Pour into large bowl; beat in vanilla and confectioners sugar until smooth. Add remaining milk 1 tsp. at a time, to reach spreading consistency. Spread half of the frosting on top of one cake layer.
To prepare topping, spoon caramel dip into a small baggie. Snip off one corner. Drizzle half over frosted layer. Top with second layer, spread remaining frosting over top, and drizzle with remaining dip, Sprinkle with pecans.