1-1/2 cups unsalted butter at room temperature
1 cup confectioners sugar
1/4 teaspoon salt
1 large egg
1 large egg yolk
1 teaspoon pure vanilla extract
3 cups flour, sifted
1-2 cups raspberry jam
Preheat oven to 350°F
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, sugar, and salt together on medium speed until light and fluffy, about 3 or 4 minutes. Scrape down the sides of the bowl and add the eggs, one at a time, beating well after each. Add the vanilla and beat to incorporate.
Turn the mixer down to low and add the flour, mixing until just barely combined.
Roll the dough into balls about 1″ diameter and place about 2″ apart on the baking sheet. These cookies will spread a bit, so they do need a bit of breathing room.
You can just make a simple indentation for regular thumbprint cookies, or you can make a heart-shape by making two overlapping indentations with your fingers.
Fill each indentation with the jam of your choice – stir it first to smooth it out. If you’d like it really smooth, you can use a food mill or sieve to remove the seeds.
Bake for about 10-12 minutes, until lightly golden brown around the edges, rotating the baking sheet halfway through the baking time. Allow to cool on a wire rack for a few minutes before removing the cookies from the pan and allowing them to cool completely.