Preheat the oven to 350F degrees. Butter 2 8-inch round cake pans, and line them with parchment paper.
In a large mixing bowl, beat together the butter and sugar until pale and fluffy. Add the eggs one at a time, beating well after each addition. Gradually add the maple syrup, stirring until smooth. Alternately add the flour and the hot water, a little at a time, stirring gently until combined and smooth. Stir in the chopped walnuts.
Divide the batter between the two prepared pans, and bake in a 350F degree preheated oven for 35 to 40 minutes, until a toothpick inserted into the center of the cake comes out clean.
Let the cakes cool in their pans on a rack for 8 to 10 minutes, then carefully unmold them and allow them to cool completely on the rack.
At this point, you can individually wrap the completely cooled cakes in cling wrap, place in an airtight container, and refrigerate or freeze them until needed. Allow the cakes to defrost completely before filling and frosting them.
Make the frosting shortly before you want to frost the cake, as it will get harder with time.
For the frosting/filling, melt the butter in a large saucepan over medium heat. Add the brown sugar and bring to a boil over medium-high heat, stirring all the while; continue to boil and stir for about 1 minute, until sugar is dissolved and mixture is thickened (watch carefully). Off the heat, and whisk in the coffee powder, the 1 tablespoon maple syrup, 2 tablespoons milk, and the maple and vanilla extracts, stirring well to combine. Allow to cool slightly, then gradually add the powdered sugar, beating after each addition, until smooth and glossy and of the desired spreadable consistency; beat in a little milk, a tablespoon at a time, if it gets too thick.
Place one of the cakes onto a cake plate or pedestal, and spoon some of the frosting/filling over the top, spreading evenly with a flat spatula; sprinkle with chopped pecans. Place the other cake on top and evenly spread the remaining frosting over the top of the cake. Decorate the top of the cake with the pecan halves. Just before serving, you may adorn the plate with autumn leaves as desired.
This cake is best eaten the day it's frosted.
Makes about 8-10 slices.