Prepare a 9x13 baking dish by rubbing in butter or spraying with non stick spray. Set aside.
In a large pot, melt butter over low/medium heat. When butter is melted, stir in marshmallows.
Continue to melt over low/medium heat until the mixture is smooth. Be careful not to overheat this mixture, as it will burn quickly.
Add a few drops of green gel food coloring until desired color is reached. Stir in rice Krispie cereal and mix with a rubber spatula until all the cereal is evenly coated.
Transfer rice Krispie mixture to the prepared baking dish and push down with a rubber spatula or your hands until it is flat and even on the top. You can spray a rubber spatula with non sticks pray to help the mixture not stick.
Let these cool for 30 minutes.
Loosen the edges with a rubber spatula and turn out onto a cutting board or parchment paper.
Cut into desired sizes, and place red hearts where desired and enjoy!
Notes
Once you add the Rice Krispies in, move quickly and mix everything together - as it can start to harden super fast.
Allow the treats to rest at room temperature and harden. You don't need to refrigerate these!
If you can't find sprinkles, just mix some red food coloring and icing, and pipe the red icing on the top of each piece.
If you love chocolate-y treats, you can also partially or fully dip them in melted chocolate, and then top them with the sprinkles.
If you're having trouble cutting these, you can grease your knife or cookie cutter with some cooking spray or butter to keep the mixture from sticking to the surface.