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 glaze combine powdered sugar and milk (or strawberry milk) in a bowl and stir with fork.
You can add red food coloring to achieve your desired color of pink or red. With a spoon, cover icing on cooled cookies and use back or spoon to spread icing to the edges. If you want to add sprinkles, cover while icing is still wet. Let icing set for a few minutes before putting in a cookie jar.