Line 2 baking sheets with parchment paper. Place the butter and icing sugar in a mixing bowl and beat with an electric hand or stand mixer until very light. Add the flour and cornstarch and beat until well combined. Press and knead the dough into a ball, and then cut into 2 pieces. Flatten one piece of dough into a 1/2” thick disc. Roll on a lightly floured surface to a 1/8" to 1/4" thickness. Dip a small, heart-shaped cookie cutter in flour and cut out cookies. Set the cookies on one of the baking sheets. Decorate the tops of the cookies with the candy decorations, gently pressing them into the dough. Chill the cookies in the fridge for 20 minutes. Repeat with the other piece of dough.
Place an oven rack in the middle position. Preheat the oven to 300 degrees F. Bake the cookies, one sheet at a time, for 12 to14 minutes, or until very pale golden on the edges. Cool on a baking rack. Store in an airtight container until ready to serve.
Note: Cake Mate heart decors, are small heart-shaped candy that are great for decorating cookies. You’ll find them in the baking supply aisle. If unavailable, use another type of red candy sprinkle to decorate these cookies.