Line a 13x9 pan with aluminum foil or parchment paper and the rub with butter or spray with cooking spray.
Place the marshmallows and butter in a large pot and heat on the stove on medium heat until completely melted. Be sure to stir continuously.
Remove the pot from the stove and stir in the cake mix and vanilla until combined completely.
Add ½ teaspoon of red food coloring and stir to combine. Add in more food coloring to get your desired color.
Add the rice krispie cereal and stir to coat completely. The mixture will be very thick.
Pour the thick mixture into the lined dish and press evenly into the corners. (use a wooden spoon or fingers if preferred)
Let stand until completely cooled (approximately 20 minutes)
Remove from the pan by lifting by the parchment paper.
Cut into rectangles or use a heart shaped cookie cutter if desired.
Store in an airtight container for 2-3 days at room temperature. up to 4-5 days if stored in the refrigerator.Use any cookie cutter shape you'd like.Use 4 cups of mini marshmallows.Substitute 7 ounce jar marshmallow crème for marshmallows.To freeze, separate layers with parchment paper or wax paper and place in a freezer safe plastic bag or container for up to a month.To make in the microwave: Add marshmallows and butter to a microwave-safe bowl. Cook for 2 minutes. Stir continuously until smooth. Then add in the cake mix, vanilla and stir to combine. Add in ½ teaspoon red food coloring and stir to combine well. Press into prepared pan.