Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, combine butter with peanut butter, granulated sugar, and brown sugar until fluffy.
Add in egg and vanilla extract, and mix until smooth. Add in the flour mixture, and mix until it is fully combined. Fold in the Christmas sprinkles.
Evenly divide the cookie dough between the lined muffin tins. Bake for 15-20 minutes. Remove from the oven and top each cookie cup with one chocolate kiss.