Pre-heat oven to 350ºF and line two baking sheets with parchment paper.
In a large bowl, whisk together flour, baking powder, and salt.
In another bowl, beat butter and sugar until pale and fluffy; about 3 minutes.
Beat in egg and vanilla; add dry ingredients in two batches until incorporated.
Using a small cookie scoop, scoop 1-inch balls onto prepared baking sheets.
Press a thumbprint, about 1/2-inch deep, into center of each ball.
Fill thumbprint with a small spoonful of jam.
Place in pre-heated oven and bake until edges of cookies are golden, 13 to 14 minutes.
Cool on baking sheets before serving.
