Cream together butter, shortening, and sugar until fluffy. Add vanilla and beat until combined.
In a mixing bowl, combine flour, baking powder, and salt. Stir to combine.
Alternate adding flour mixture with milk until combined.
Whisk egg whites until soft peaks form.
Fold egg whites into petit fours batter, and stir until just combined.
Heat oven to 350 degrees F.
Spray baking pan with PAM Cooking Spray.
Bake for 5 to 10 minutes or until lightly golden (or a toothpick inserted comes out clean). My mini heart pan was very small, so 5 minutes was perfect. Watch your oven carefully.
Allow to cool before glazing.
To make glaze, combine powdered sugar, corn syrup, and extract in a double boiler, and heat until smooth. This might take a little time to heat up; just stir periodically.
Once smooth, dip hearts upside down in glaze, then return to wire rack to allow to cool. Decorate with a heart sprinkle. You can also heat up your glaze even further to make the glaze more “pourable” if preferred.