Begin by combining the softened butter, cream cheese, milk, and granulated sugar in a medium-sized bowl. Use an electric mixer to beat the ingredients together until they are thoroughly blended and the mixture becomes smooth. Then, add in the egg yolk and continue beating until well combined.

Next, sift together the all-purpose flour and baking powder. Gradually add this dry mixture to the bowl containing the butter mixture. Stir until the ingredients come together to form a stiff dough. Ensure that all the flour is fully incorporated into the dough.

Cover the bowl with plastic wrap or a lid, then refrigerate the dough for several hours or overnight. Chilling the dough will help it firm up and become easier to handle when rolling out.

Once the dough has chilled sufficiently, preheat your oven to 400°F (200°C). Line baking sheets with parchment paper or lightly grease them to prevent the cookies from sticking during baking.

On a lightly floured surface, roll out the chilled dough to a thickness of about 1/4 inch. Then, use a floured 2-inch cookie cutter to cut out individual cookies from the rolled dough. Place the cookies onto the prepared baking sheets, leaving some space between each one.

Using your thumb or the back of a spoon, gently press an indentation into the center of each cookie. Spoon approximately 1 teaspoon of Solo Raspberry Fruit Filling into the indentation of each cookie, ensuring they are evenly filled.

Transfer the baking sheets with the prepared cookies into the preheated oven. Bake for 10 to 12 minutes, or until the edges of the cookies are lightly golden brown. Keep an eye on them to prevent over-browning.

Once baked, remove the cookies from the oven and transfer them to wire racks to cool completely. Once cooled, sprinkle the tops of the kolacky cookies with powdered sugar for a decorative finish.

Arrange the solo kolacky cookies on a serving platter and serve them to family and friends. These delightful treats are perfect for enjoying with a hot cup of tea or coffee, or as a sweet snack any time of day. Enjoy!