Preheat oven to 225°F. Line 2 baking sheets with parchment paper. Place oven racks in top and lower thirds of the oven.

In a medium bowl combine sugar, cornstarch, and baking powder. In a large bowl beat egg whites and cream of tartar with a mixer on medium until soft peaks form (tips curl). Increase mixer to high speed, adding sugar mixture, 1 Tbsp. at a time, over a 2 minute period, until mixture still forms soft peaks.

Reduce mixer speed to medium. Beat in the extract to combine. Using a thin wooden skewer, add two to three stripes of food coloring to the egg white mixture at different places. Run a metal spatula through the food coloring 1 to 2 times to create streaks. (The color will continue to incorporate as you portion out the meringues.)

For each heart, spoon 2 to 3 Tbsp. of the meringue mixture on a prepared baking sheet into two ovals that overlap slightly. Dip a spoon in water and bring ovals together, pulling to form the tip of the heart. Repeat with the remaining meringue mixture, spacing hearts 2 inches apart.

Bake until crisp and dry, 1 1/2 hours, rotating the pans from top to bottom and from front to back halfway through baking. Turn oven off. Let stand 30 minutes in oven. Remove and cool on wire racks.