• Mix the butter, granulated sugar, and brown sugar until creamy. Add the egg and vanilla extract and mix until fully incorporated. Add 2 tablespoons of sour cream and mix well. Finally, add the flour, baking powder, and salt. Mix until a smooth dough forms.
• This dough is stickier than you might be used to with cookie dough; there’s no need to firm it up by adding extra flour.
• Form small balls from the dough. If you have a set of measuring spoons, use 1 full tablespoon of dough per ball. Don’t have one? Just aim for balls about the size of a large marble.
• Because the dough is quite sticky, it helps to lightly grease or dampen your hands.
• Bake the cookies for 15 minutes at 180°C/350°F until the bottoms are golden brown. The cookies themselves will remain fairly light in color.
• Once the cookies have cooled, you can fill them. Spread a small amount of preserves on one cookie; about a small teaspoon is enough. Gently press another cookie on top and place it on a plate. Repeat until all cookies have been turned into sandwich cookies.
• Another common method (which I didn’t use) is to hollow out the cookies slightly so you can add more filling. I think that makes them even tastier, but it’s definitely not required.

Decorating the cookies

• Take two small bowls and add a small splash of milk to each. Color one with red food coloring and the other with yellow. Don’t be too stingy with the coloring, or it’ll be difficult to get good color on the cookies.
• Start with the yellow coloring. Use a brush to color the edges of the cookie. Make sure you cover the entire edge; it’s fine if you touch the filling. Then color the center, leaving a few spots uncolored.
• Fill in those uncolored spots with the red coloring, and feel free to blend in a little yellow as well. Continue until you’re happy with the design.
• Color the other cookie the same way, then dip it into the granulated sugar.
• Place the cookies on a plate and let them dry.