Cake: Preheat the oven to 350 F and line the bottom of a jelly roll pan (~13 x 18 inch) with parchment paper. Grease the sides of the pan.
mix the hot water with the cake mix. Add the rest of the cake ingredients and mix on low for 1 minute. Scrap down the bowl and beat on medium for 2 minutes, until the batter is paler brown in color.

Cake: Transfer the cake batter to the jelly roll pan and smooth the top. Bake for 13-15 minutes. The cake is done with a toothpick inserted in the center of the cake is clean. Let the cake cool in the pan. The cake will stay in the pan.

Frosting: After the cake has finished baking and has cooled, prepare the frosting. Beat the butter and cocoa powder together for ~30 seconds. Scrap the bowl and add the rest of the frosting ingredients. Beat ~1-2 minutes on medium, until the frosting is fluffy and paler brown in color. Using an offset spatula, smooth the frosting over the top of the cake. The cake can be refrigerated at this point or kept at room temperature.

Pecan topping: Mix the brown sugar and cornstarch together in a bowl. Melt the butter in a small saucepan and then add the milk, corn syrup, and brown sugar mix. Let the mixture come to a simmer, then continue to simmer for ~1-2 minutes until it thickens. In a separate bowl, combine the pecans, coconut, and vanilla. Pour the sugar mixture over the pecans and mix well. Let the mixture cool to room temperature, stirring occasionally.

Pecan topping: Drop by tablespoonful the pecan topping onto the frosted cake. Use an offset spatula to spread the mixture evenly over the top, working across the whole cake.