In the bowl of your stand mixer cream together brown sugar, granulated sugar and butter over medium speed. Add the egg and vanilla extract.
Add the flour, salt, and baking soda and mix over medium speed until all ingredients are well incorporated.
Wrap your dough in plastic wrap and place in the fridge for 30-45 minutes to chill.
While your dough is chilling, place strawberry jam on the counter to get to room temperature and whisk to loosen up.
Preheat oven to 375 degrees.
Line a baking sheet with parchment paper and roll about 1.5 tbsps of dough into a ball and place on the sheet.
Using your thumb or index finger, gently press the center of each cookie dough ball. Be sure NOT to press all the way through to the bottom of the cookie.
Fill each thumbprint with about a 1/2 tsp of jam.
Bake cookies for 9-11 minutes until lightly golden on bottom and toothpick runs through the cookie clean.
Transfer cookies to cooling rack and let cool completely. Sprinkle with powdered sugar.