Place the butter, sugar and brown sugar in a large mixing bowl.
Beat with a mixer until light and fluffy, about 3 minutes.
Add the egg and vanilla.
Beat until combined.
Add the in the dry ingredients.
Beat until well blended.
Form the dough into a ball and cover with plastic wrap.
Refrigerate overnight.
Remove the cookie dough from the refrigerator about 10 minutes before you plan to use it.
Preheat the oven to 375 degrees.
Cover 2 cookie sheets with parchment paper.
Roll the dough into 1-inch balls.
Roll the balls in Christmas sprinkles if desired.
Place the balls of dough 3 inches apart on a cookie sheet.
Use a small,rounded measuring spoon or your thumb to make an indentation in the middle of each cookie.
Fill each cookie with ½ teaspoon of jam.
Chill the cookies for 15 minutes.
Top with sprinkles if desired.
Bake for 10-11 minutes or until light golden brown around the edges.
Let sit for 5 minutes, then transfer to a wire rack and cool completely.
Dust with powdered sugar, or drizzle with a powdered sugar glaze or melted white chocolate chips.
Notes
Storage:Let the cookies cool to room temperature before placing 'em in an airtight container. Raspberry jam thumbprints will keep for 4-5 days on the counter.If you'd like to freeze leftover cookies for an easy, last-minute treat, flash-freeze them on ungreased cookie sheets or a plate. Once solid, gently toss 'em into a bag and freeze for up to three months. Tips:
Let the butter sit at room temperature for about an hour (a little more if your kitchen is cool) to soften.
For best results, don't skip the chilling time.
The jam will bubble up a little in the oven, so don't overfill each thumbprint cookie.
If you like soft cookies, take them out of the oven sooner rather than later. Thumbprint cookies will get crumbly quickly if you overcook them.