In a large mixer, stir butter and sugar together until blended. Stir in egg and vanilla. Scrape sides of bowl and mix again. Slowly stir in flour and baking powder until just incorporated. Dough will be crumbly so you'll have to work it together with your hands. Shouldn't take too much effort.
Roll dough out to be 1/4-3/8 inch thick on a well-floured work surface.
Cut into heart shapes and transfer to a baking sheet.
Stamp phrases onto cookies and freeze 10 minutes.
Immediately transfer to oven and bake 8-10 minutes. The thicker the cookie, the longer the baking time. Cool 3 minutes, then transfer to cooling rack. Serve at room temperature. Store any extra cookies in an airtight container for up to 4 days.