I found this off Pinterest and just had to try it.
Frosted Cake Batter Blondies
-1 white or yellow cake mix, or funfetti mix
-1/4 cup vegetable oil
-1/2 cup milk (I used almond milk)
-1/2 cup white chocolate chips
-1/2 cup mini marshmallows (I omitted)
-1/4 cup sprinkles (unless you used a funfetti mix)
Preheat oven to 350. In large bowl, combine mix, oil, egg and milk. Stir in chips and marshmallows. Batter will be thick. Spread in prepared pan and bake for 25 minutes, until center is just set.
-1/2 cup butter, room temp (I used Earth Balance dairy and soy-free spread)
-2 cups powdered sugar
-1/2 cup marshmallow fluff
-1 Tbs milk
Mix butter and marshmallow fluff until smooth. Slowly add powdered sugar, mixing slowly. Add milk and mix on medium until smooth. Frost cooled blondies. Top with sprinkles.
I got antsy and put the frosting on while the blondies were still warm, so they didn't firm up as well as they should. They're super rich and sweet, so a little bit will go a long way but they are oh so tasty!