Make the Syrup: Combine blueberries, water, and sugar in a small pot. Bring to a boil, then simmer for 3-5 minutes until the berries pop and the liquid turns into a dark purple syrup.
Prep the Bread: Trim the crusts off your bread slices. Line the bottom of an 8x8 pan with a single layer of bread, cutting pieces to fit so there are no gaps.
Layer: Spoon half of the hot berries and syrup over the bread. Make sure the bread is completely soaked! Add a second layer of bread on top, then pour over the rest of the berries and syrup.
Press: Place a piece of plastic wrap over the top of the bread. To weight it down, use a smaller pan (like a loaf pan or a 7x7 square), a small cutting board, or even a flat plate that fits inside the 8x8 pan. Place a few heavy soup cans on top of that to provide the pressure. This "presses" everything together into a fudge-like texture.
Chill & Serve: Refrigerate with the weight on for at least 4 hours (overnight is even better). Slice into squares and serve cold with a big scoop of vanilla ice cream or a dollop of whipped cream.
