In a large mixing bowl, combine the flour, baking powder, salt, sugar, and cinnamon, if using.
In a separate bowl, combine the melted butter, milk, beaten eggs and vanilla.
Blend the liquid ingredients into the flour mixture using an electric hand mixer or wooden spoon until combined. Avoid over-mixing.
Fold in the chopped nuts - except for those reserved for the top.
Preheat the oven to 375°F.
Pour the cake batter into a lightly greased 8"x12" rectangular pan, a 9"x 9" square pan or a 9" Pyrex pie pan, spreading the batter evenly. Sprinkle the reserved chopped nuts evenly over the top of the batter.
Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean.
Place pan on a wire rack. Cool completely.
To serve, cut into squares or wedges, depending on which shape pan you've used.