Into a large bowl, whisk together flour, baking powder, cinnamon and salt.
In a large mixing bowl, beat together butter and sugar until light and fluffy. Mix in the eggs, one at a time, until combined. Mix in vanilla. Add the flour mixture in two parts, alternating with the milk - beginning and ending with the flour. Fold in the walnuts.
Evenly divide the mixture between 2 12 cup muffin tins (about 1/3 cup per cupcake) lined with paper liners. Bake, rotating pans halfway through, until golden and the tops spring back when lightly pressed in the center, about 16 to 20 minutes. Remove and place on a wire rack to cool for a couple mixture. Carefully turn the cupcakes out and reinvert on a cooling rack so their top sides are up.