Peanut Butter and Jelly Thumbprint Cookies
With your electric mixer beat the butter and both sugars (reserving the 1/4 cup white sugar for later) on medium speed for 5 minutes, scraping the bowl occasionally, until light and fluffy. Add the peanut butter and beat until smooth. Add the egg and vanilla and beat until well combined.
In a separate bowl, combine the flour, baking soda and salt. Reduce the mixer speed to low and add the flour mixture in 3 additions, alternating with the milk. Mix just until combined.
Place the dough in the refrigerator to chill for 1 hour until firm enough to roll into balls. Roll rounded tablespoons of cookie dough into balls, then roll the balls in the remaining 1/4 cup sugar. Place on a cookie sheet (you can put them close together to fit them all on one sheet for this step). Freeze dough balls for 1 hour.
Preheat the oven to 375 F. Working in batches, place the frozen cookie balls 2 inches apart on an ungreased baking sheet (don't use parchment or a silpat, or they may spread too much, and you want them to stay small, round and puffed). Keep the remainder of the cookie balls in the freezer until you're ready to bake them.
Bake the cookies for 7 minutes. Remove from the oven and, working quickly, press an indentation in the center of each cookie using the back of a teaspoon measuring spoon. Fill the indentations with the jam (To be able to do this as quickly as possible, I first warmed the jam in the microwave for 30 seconds, stirred until smooth, then spooned the jam into a small squeeze bottle to quickly and easily fill the cookies.) Return the cookies to the oven and bake for an additional 2 minutes.
Cool the cookies on the pan for 1 minute, then transfer to a wire rack to cool completely. They may appear to be too soft and unbaked, but trust me, they'll set up as they cool, and the following day they'll be so soft and yummy that you may just want to cry out of happiness!
Notes: The dough can also be prepared and refrigerated for several weeks ahead of time. Baking the jam in the last two minutes sets the jam a little so that it won't be too messy later, and you should be able to stack the cookies to store them in an airtight container without messing up the jam. Instead of jam, try a little Nutella. Or, for one of my favorite cookies, press a Hershey's kiss into the center of the cookie after it's baked.
Yields 3 dozen cookies.