Preheat oven to 375˚F.
In a stand mixer or with a hand mixer cream together butter and sugar.
Add milk, egg and vanilla and continue to mix. Scrape down sides of the bowl.
In a mixing bowl, whisk together flour, baking powder and salt.
Pour flour mixture into the butter mixture and mix until evenly blended and a dough forms.
Divide dough into two discs, wrap in plastic wrap and refrigerate for 1 hour.
Lightly flour a clean surface. Roll out 1 disc of dough to ⅛ inch thickness. Using a 4-inch heart shaped cookie cutter punch out about 9 heart cookies.
Transfer cookies onto a parchment lined baking sheet, 1 inch apart. (You will need multiple baking sheets or will need to bake cookies in batches).
Repeat steps 7 and 8 with other half of dough.
Bake cookies for 8 to 10 minutes or until cookies barely begin to brown around the edges.
Remove baking sheet from oven and allow cookies to rest for about 5 minutes before transferring onto a cooling rack.