The night before: Peel the oranges using a wide vegetable peeler. Pour the gin into a large glass or metal container, and express the oil of all the peels right onto the surface of the gin, dropping the peel into the gin afterwards. Cover with plastic wrap and let it sit out at room temperature overnight. Pull the orange juice concentrate out of the freezer and let sit out overnight as well, so it's thawed out by game time. Freeze a bundt cake pan full of water, or another large container, in order to obtain a sizable ice block.
The day of: Strain gin into punch bowl and discard peels. Add Lillet, orange juice, concentrate, Campari and Grenadine. Whisk to combine until concentrate is fully incorporated. Keep in fridge until 15 minutes before the party starts. Then add ice block, fruit and sparkling wine, and give it a final stir. Serve in small cups, over ice.
Photo courtesy of Trenchermen