Thumbprint cookies are quite deceiving. They look fancy, and yet they are completely easy to make. The best part about them is how adaptable they are based on the filling you choose. We find... that jams with “no sugar added” are still plenty sweet from the natural fruit sugars, and we recommend using those.
In a separate medium bowl, stir together whole wheat flour, all-purpose flour, salt, and baking powder. Turn the mixer on low speed and gradually add the flour to the butter mixture. Mix just until the flours are incorporated.
In the bowl of a stand mixer (or use a hand mixer), cream butter and sugar together. It should look fluffy and take about 5 minutes. Add the vanilla.
Bake for 20 to 25 minutes or until the edges are golden brown. Let cool and serve.