In a large bowl with a handheld electric mixer (or in an electric stand mixer), cream together the butter and sugar for 1-2 minutes. Add the egg and vanilla and mix until well combined.
Add the flour, baking powder, and salt. Mix until combined; the mixture will be in little pieces.
In a separate bowl, stir together the sour cream and baking soda. The sour cream may foam a bit - that's totally normal.
Add the sour cream mixture to the cookie dough and mix until combined. Don't overmix - just until it is smooth and looks like sugar cookie dough.
Wrap the dough in plastic wrap and refrigerate for 1-2 hours.
Preheat the oven to 375 degrees F.
Roll the dough on a lightly floured counter to about 1/4-inch thick and cut into desired shapes, using additional flour on the counter or rolling pin as needed. Place the cutout cookies on a parchment lined baking sheet a couple inches apart and bake for 9-11 minutes, depending on the size and thickness of the cookies. Do not over bake. They'll be puffed up a bit and should be lightly browned (or not browned at all) on the bottoms; they'll be softer if there's no browning on the sides and top.
Let the cookies rest a few minutes on the baking sheet before removing to a wire rack to cool completely before icing.
For the smooth icing: combine powdered sugar and milk in a bowl and stir with fork until smooth. Add corn syrup and almond extract and stir until combined.
Divide icing into two bowls and add red and green food coloring to achieve your desired shade.
Once cookies have been cooled dip cookies upside down into icing for a smooth finish. If you want to add additional designs use white buttercream icing with a small tipped bag. Add sprinkles while icing is still wet. Let icing set for a few minutes before putting in a cookie jar or plate. Enjoy with a glass of ice, cold milk.