This is a close relative of the Purple Cow. My kids came up with this when their Daddy was going on his first ever liquid only fast.
1 can of frozen 100% orange juice concentrate
Saved can from OJ, filled with milk
Pour (or scrape) the frozen OJ into a blender. Next use the can from the OJ, filled with milk, and pour the milk into the blender. Fill the remaining space with ice cubes (about one tray's worth). Then blend until slushy.