Preheat oven to 180 C / Gas 4. Grease and line two sandwich tins.
Beat butter and sugar together until light and fluffy, then add the eggs, one at a time. Sift in the flour and baking powder, mix until combined, add milk and then stir in the pecans. Divide between the two tins.
Bake for 20 to 25 minutes, or until a skewer inserted in the centre comes out clean. Remove from oven and let cool.
Buttercream: Beat together butter and sugar, add milk, then maple syrup and beat until smooth.
Sandwich the cooled cakes together with buttercream, saving some for the top. Decorate with any leftover pecans and a drizzle of maple syrup.