Heat oven to 350 degrees. Spray a 9x13 baking dish with cooking spray or line it with parchment paper. Set aside.
In large mixing bowl, combine the dry sugar cookie mix, dry cake mix, eggs, melted butter, and vanilla extract. Beat with a handheld blender until combined. About 1 minute.
Add in the sprinkles and very gently (so the colors don't bleed) stir in the sprinkles using a wooden spoon or spatula.
Dump the batter into the prepared baking dish and spread out evenly. It helps if you drop it all over the baking dish, instead of just one big pile. Use your hands to help spread it out.
Cook for 30-32 minutes. Edges will be golden brown and puffier than the rest of the bars. The center will look done and a toothpick inserted into the middle should come out clean. Let cool completely for about 1 hour in the pan.
To make frosting : Use a handheld blender and beat the butter in a mixing bowl until creamy. Add in the powdered sugar, almond extract, and start with 1 tablespoon milk. Blend together and add additional milk until you get a spreadable consistency. They higher fat milk you use, the more you may need. If you use skim or 1% milk you will need less of it.
Spread the frosting over the cooled cookie bars. Sprinkle some additional sprinkles over top the frosting. Cut into bars right away and serve or they can be refrigerated (if wanted) or left at room temperature, until you serve them.