1. Preheat oven to 350 degrees. Line two standard 12-cup muffin pans with paper liners. Into a large bowl, sift together flour, baking powder, salt, and cinnamon; set aside.

2. In the bowl of an electric mixer fitted with the paddle attachment, beat butter and sugar on medium speed until creamy, about 3 minutes. Add the eggs and vanilla, and beat until combined. With the mixer still on medium speed, add the flour mixture in two parts, alternating with the milk and beginning and ending with the flour. Stir in walnuts with a wooden spoon.

3. Divide the batter evenly among the muffin cups, filling each three-quarters full. Bake, rotating pans halfway through, until cupcakes are golden and a cake tester inserted in the center of a cupcake comes out clean, 18 to 20 minutes. Transfer the pans to a wire rack to cool slightly. Invert cupcakes onto the rack; then reinvert and let them cool completely, top sides up. Frost tops with Maple Buttercream and garnish with candied walnuts, if using. Cupcakes can be refrigerated in an airtight container for up to 3 days.