Wash your hands well, then mix sugar, peanut butter, and egg together in a large bowl.
Stir raspberry preserves in a separate small bowl until smooth, to avoid chunks in your fruity filling.
Pour some granulated sugar on a plate, then roll your peanut butter dough into balls and roll each in sugar.
Arrange your cookies on a greased baking sheet (or use silicone baking mats), then use your thumb to press a well into the center of each. (If the edges crack, just gently press the dough back together.)
Fill the center of each cookie with raspberry preserves.
Bake at 350 degrees for 14 minutes, or until bottoms are brown.
Let cool slightly before removing from baking sheets.
We baked ours on two separate cookie sheets and swapped oven racks and flipped pans around halfway through. This is a crumbly cookie and the tops won't get especially brown, but they're cooked through when the bottoms are browned. Naturally gluten free and dairy free!
Easy Flourless Peanut Butter & Jelly Thumbprint Cookies from Mashup Mom: https://www.mashupmom.com/easy-flourless-peanut-butter-jelly-thumbprint-cookies/