Start by preheating your oven to 325°F (165°C) to ensure it’s ready for baking. In a stand mixer fitted with the paddle attachment, cream together 1 cup of salted butter, 1 cup of white sugar, and 1/2 teaspoon of baking powder on medium speed until the mixture is light and fluffy, which should take about 3 to 4 minutes.

Scrape down the sides of the bowl to ensure even mixing. Add 1 large egg to the butter mixture and beat well until fully incorporated. Then, add 2 teaspoons of pure vanilla extract and mix until everything is combined.

With the mixer on low speed, gradually add 2-1/2 cups (312g) of all-purpose flour. Mix until the ingredients are just barely combined to avoid overworking the dough, which can make the cookies tough.

Roll the dough into balls about 1 inch in diameter and place them at least 1 inch apart on a baking sheet to allow room for spreading. Immediately make an indentation in the center of each ball using your thumb or a rounded tool to create a space for the filling.

Fill each indentation with your choice of jam, using approximately 1 cup in total. Slightly overfill each to accommodate for spreading during baking. Place the cookies in the preheated oven and bake for about 20 minutes. Halfway through the baking time, rotate the baking sheet to ensure even baking.

Once baked, allow the cookies to cool for a few minutes on a wire rack before removing them from the pan. This helps them set and prevents them from breaking apart. Continue cooling the cookies on the rack until they reach room temperature. Enjoy your delicious, freshly baked thumbprint cookies!