1/4cupjam in the flavor of your choosingpreferably seedless
powdered sugar for dustingif desired
Line a large baking sheet with parchment paper or a silicone baking mat. Set aside. Make room in the refrigerator to store the baking sheet for a few hours.
In a large bowl with a handheld mixer or the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar on high speed until light and fluffy (approximately 2 minutes). Decrease speed to medium and beat in the vanilla extract and salt. Scrape down the sides and the bottom of the bowl as necessary.
With the mixer on low, slowly add the flour into the wet ingredients and mix until soft dough is formed. Dough will be slightly crumbly. This is ok. Press the dough and all of the crumbs into a ball in the bowl.
Using a cookie scoop or a Tablespoon measure, roll the dough into 1" balls with your hands. Place the dough balls far enough apart that they can spread. I baked mine in 4 rows of 3. Once you have filled a baking sheet, use your thumb to make an indentation in each dough ball. Dough balls will likely crack, and this is totally fine. You may smooth the cracks with your fingers if you wish. Place baking sheet in the refrigerator for at least 2 hours or up to 3 days. If chilling longer than a few hours, cover with plastic wrap.
When you are ready to bake the cookies, preheat oven to 350ºF.
Remove the baking sheet from the refrigerator. Fill each thumbprint with jam (approximately 1/2 - 3/4 teaspoon).
Bake cookies for 12-14 minutes, or until very lightly browned on the edges. Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Dust with powdered sugar, if desired, before serving. Cookies stay fresh in an airtight container at room temperature up to 1 week.