In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and sugar together on medium speed until light and fluffy, about 3 or 4 minutes.
1 cup (227g) unsalted butter, 1 cup (200g) white sugar
Scrape down the sides of the bowl and mix in the egg, vanilla and almond extract (if using) until incorporated.
With the mixer on low, stir in half flour until just combined. Repeat with the remaining flour.
Roll the dough into 1" balls and place about 1" apart onto the prepared baking sheets. Using the end of a wooden spoon dipped in flour, 1/4 tsp measuring spoon, or your thumb, make an indent halfway down each cookie.
Fill each indentation with the jam of your choice. Slightly overfill so that's it's rounded on top because the jam will flatten out as the cookies bake.
1 cup jam
Bake for 15-20 minutes or until the edges just start to brown. Let cookies cool enough to touch before transferring to wire rack.
Notes
Leftover cookies can be stored in an airtight container at room temperature for 3-5 days.