Beat the cream cheese and butter. In your mixer's bowl, beat the cream cheese and butter until smooth, light, and fluffy.
Add the dry ingredients. Add the flour and salt and continue to mix until thoroughly incorporated.
Shape the dough. Lightly dust your work area with powdered sugar. Transfer the dough to the work area and shape it into a ball.
Chill. Divide the dough into 4 rounds; flatten each round and cover each round of dough with plastic wrap. Refrigerate for 30 minutes.
Make the cheesecake filling. In the meantime, prepare the filling by combining the cream cheese, powdered sugar, and vanilla in your mixer's bowl. Beat until creamy and smooth. Set it aside.
Roll and cut the dough. Dust your work area with flour. Remove the dough from the fridge and let it rest for 5 minutes. Afterward, roll out each ball of dough to a 1/4-inch thickness. Then, cut it into 3x3 squares.
Add the fillings. Fill the center of each square with 1/2 teaspoon cream cheese mixture and 1/2 teaspoon strawberry jam. For a prettier presentation, using a pastry bag, you can pipe the fillings, one next to the other or one over the other.
Fold. Overlap opposite corners of the dough to the center and over the filling. Pinch the seams together. Refrigerate the cookies for 1 hour.
Bake. Preheat the oven to 375ºF. Remove the cookies from the fridge and bake them for 10 to 12 minutes or until the edges are browned. Remove from the oven and cool completely.
Notes
Cream Cheese: This recipe works best with full-fat cream cheese. Make sure it is softened before you start to work with it.
Butter: Use two sticks of softened unsalted butter. That is 16 tablespoons or 226 grams of butter.
Jam Filling: You can use whatever jam or preserves you have on hand. In fact, for a more authentic kolacky, you don't even have to make the cream cheese filling - just use the jam.
Do not skip the refrigeration time before rolling out the dough AND before baking the pastries.
Store the pastries in airtight containers and keep them refrigerated. You can also freeze the cookies for up to 3 months. I suggest freezing them filled but not baked. When you need them, you can thaw them on the counter and then bake them as needed.