Heat oven to 350°F. In small bowl, combine flour and baking Powder.
In large bowl, beat together peanut butter and butter until smooth. Beat in sugars, egg and vanilla until blended. Stir in flour mixture until blended. Shape dough into 30 balls.
Place coloured sugars in small bowls. Roll dough balls in coloured sugars and place 2-inches apart on parchment lined cookie sheets.
Bake 8 to 10 minutes or until edges are light brown. Immediately press one chocolate heart in centre of cookie. Remove to a wire rack. Cool completely.