Preheat the oven to 350 degrees.
Combine the butter, flour, baking powder, vanilla and crushed nuts in a mixing bowl.
Scoop dough by the rounded tablespoon full and roll each scoop into a ball.
Arrange the cookie balls on an ungreased baking sheet and make a depression in the center of each with your thumb.
Bake 10-14 minutes, or until the bottoms are golden.
While cookies are cooling, make the icing.
Melt the butter in a small mixing bowl. Add the vanilla and powdered sugar and stir to combine. Add milk 1 tsp at a time to make a smooth but reasonably thick icing.
Divide icing into two small bowls and add a couple of drops of red food coloring to one, green to the other, mixing each thoroughly. Add milk, 1 tsp at a time, as needed, to thin the icing out.
Drizzle icing into the depression at the center of each cookie, alternating red and green. (Make additional icing if desired).