In a medium mixing bowl combine the flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer beat the butter until smooth. Gradually add in the sugar and continue mixing on medium until fluffy.

Add in the egg and vanilla and beat until mixed well.

Place the mixer on low and add in the flour mixture, mixing until just blended.

Knead the dough into a ball and flatten into a disc shape. Cover with plastic wrap and refrigerate for at least an hour or overnight.

Preheat the oven to 375 degrees.

On a lightly floured surface roll the dough to 1/4 inch thick. Cut out 30 Christmas trees. Place the cookies on a baking sheet and bake for 8-10 minutes or until they no longer look wet on top.

Remove from the oven and allow to cool for 2 minutes on the cookie sheet before removing to a wire rack. Cool completely.

To make the buttercream frosting place the butter in a mixing bowl and use a mixer on medium high speed to beat the butter.

Add in the powdered sugar a half cup at a time, beating after each addition.

Add the milk and vanilla and beat on high for 1 minute.

Add the green food coloring and mix well.

Place the green frosting in a piping bag without a tip. Snip off the end and move your hand back and forth to pipe the frosting onto the tree.

Immediately top with sprinkles if desired.

Let the cookies sit for at least 1 hour so that a crust begins to form on the buttercream frosting and you can move the cookies without damaging them.