Preheat oven to 350 degrees Line 2 baking sheets with parchment paper.
In a medium size bowl, whisk the flour, baking powder and salt together.
In another bowl, whip the butter and the sugar with a hand-held mixer until fluffy, about 5 minutes.
Beat in the egg and vanilla until just combined. Slowly beat in the dry ingredients in 2 additions, mixing just until incorporated.
Scoop the dough into 1-inch balls with a cookie scoop and roll in sugar.
Place the cookies about 2-inches apart on the prepared baking sheets.
Press a thumbprint into the center of each ball, about 1/2-inch deep.
Fill each indentation with about 3/4 teaspoon jam.
Bake cookies until the edges are golden, about 15 minutes.
Cool cookies on the baking sheets.