In a medium bowl, lightly mash 1 cup of berries with a potato masher or wooden spoon.
Fold in sugar, lemon zest and juice and stir until a syrup begins to form.
Fold in remaining 2 cup of berries until everything is well coated, then let sit at room temperature for 1-2 hours.
Once berries are ready, preheat the broiler to high and move your top oven rack as close to the broiler as possible.
Place toast slices on a baking tray and top with slices of brie, letting the edges hang off a bit.
Broil for about 30 seconds, keeping a close eye so the cheese doesn't melt too much.
Once brie is soft and lightly bubbling, remove from the oven and transfer toasts to plates.
Top with a smattering of macerated berries and serve immediately, along with plenty of napkins.
