Combine soda, grenadine, and vinegar and let stand for a few minutes. Add sugar and oil and whisk vigorously until slightly frothy. In a separate bowl, mix flour, baking soda, and baking powder. Add flour mixture to the first bowl. Be careful not to over-mix.
Fill cupcake liners about 1/2 way. They will rise a lot! Bake for 20 minutes at 350 degrees.
Lemon-lime cream cheese frosting Instructions
Make sure butter and cream cheese are at room temperature. Cream the butter and cream cheese. Sift in 4 C of powdered sugar. Add extracts.
Concentrated Grenadine Instructions
Mix equal parts of grenadine and powdered sugar to make the grenadine more of a syrup, less runny. If the sugar isn't dissolving in the grenadine, you may need to heat it on the stove on low heat until it dissolves. Add a few drops of red food coloring to the homemade grenadine if you want the hearts to be a deeper red.
Pour the grenadine syrup into the heart. The frosting will act as a wall keeping the syrup within the boundary of the heart. Because the cupcake is porous, the syrup will seep through into the cupcake. This is what makes the cupcake so yummy! As the syrup seeps in, add more. I added 3 or 4 layers of grenadine to mine. Eventually, you should be left with the center of your heart dyed red.