Line a baking sheet with parchment paper and preheat the oven to 425 degrees.
Whisk together flour and sugar in a large bowl.
Add the butter and cream cheese to the bowl and use a pastry cutter or 2 knives to cut them into the flour until the mixture is crumbly and there are no pieces larger than a pea.
Stir in buttermilk and sprinkles until a shaggy dough forms.
Turn dough out onto a lightly floured surface. For easy clean up, I lay a piece of parchment paper on the counter and lightly flour it.
Pat dough into a rectangle and cut into 4 pieces. Stack the pieces and flatten them down until you have 1 piece of dough that is about 1-inch thick.
Repeat this process, cutting into 4 pieces and stacking them, 3 more times.
Pat or roll dough until 1-inch thick. Use a knife to cut into 2-inch squares. Place biscuits on prepared pan. Brush tops with egg.
Bake 12 to 15 minutes or until golden brown.
To make glaze, whisk together all ingredients except sprinkles. Drizzle on top of biscuits and sprinkle with extra sprinkles.