Heat the oven to 350°F. Line baking sheets with parchment.
Stir together the melted butter, peanut butter, granulated sugar, and brown sugar until smooth. Cool a few minutes if warm.
Beat in the eggs and vanilla.
Whisk the flour, baking powder, and salt. Stir into the wet ingredients to make a stiff dough, adding more flour if needed.
Shape into 2-inch balls and roll in the remaining sugar. Place 2 inches apart on the sheets.
Bake 10 to 12 minutes, until the edges are set and the tops crack slightly.
Immediately press a chocolate kiss into the center of each cookie.
Cool on the pan for a few minutes, then move to a wire rack until the chocolate is set.