Prep time: 20 minutes
Cook time: 11 minutes
Serving size: approximately 24 cookies
Keeps for up to 1 week in an airtight container
For the cookies:
-225g room temperature butter
-1/3 cup sugar
-1/3 cup brown sugar, tightly packed
-1 egg yolk
-3/4 tsp vanilla extract
-2 1/4 cup all-purpose flour
-2 tsp cornstarch
-1/2 tsp salt
-1/2 cup sugar, for rolling (optional)
For the filling:
-jam or preserve of your choice
Place the butter in the bowl of a stand mixer (you can use a large bowl and hand mixer instead) and beat until creamy.
Scrape down the sides of the bowl, add sugars, and beat, gradually increasing mixer speed to medium-high until ingredients are well-combined), about 30-60 seconds.
Add egg yolk and vanilla extract and beat well. In a separate bowl, whisk together the flour, cornstarch, and salt.
With the mixer on low speed, gradually add the flour mixture to the wet ingredients until completely combined. This dough will seem very dry and crumbly, so be sure to pause occasionally to scrape the sides and bottom of the bowl. If it starts to strain the mixer, you can use your hands to finish working the dough together.
Scoop cookie dough into 1 tbsp-sized balls and roll very well (so that the dough is round and that there are no cracks).
Roll in the granulated sugar (if you're using it) and place on a wax-paper covered plate or small cookie sheet. Use your thumb or the rounded back of a teaspoon to gently press an indent in the center of the cookie dough. Repeat until all the dough has been used.
Transfer the cookie dough to the freezer and chill for 30 minutes. Once the dough is done chilling, preheat the oven to 375F/190C and place your jam in a small, microwave safe bowl. Heat briefly or until the jam is not hot but is no longer firm and easy to stir.
Spoon the jam into each thumbprint, filling each indent to the brim.
Once the oven is preheated, place the cookies at least 2' apart on the parchment paper-lined cookie sheet and bake at 375F/190C for 11 minutes or until the edges turn golden brown. Allow the cookies to cool completely on the baking sheet before eating. Enjoy!!