Prepare a fire or grill for medium-low heat and set a grate over it. Alternatively, you can prepare this on the stovetop.
Place the berries in a large bowl. Add the sugar and gently toss the berries to thoroughly coat.
Pour the berries into a 9- or 10-inch (23 or 25 cm) cast-iron skillet and dot with the butter. Set the pan on the grill grate or on the stovetop over medium heat and cook until the sugar melts and the berries begin to caramelize, 5 to 6 minutes. Stir occasionally as the butter melts into the caramelized sugar and berries and forms a sauce.
Remove the skillet from the heat and strain the sauce into a bowl, leaving the berries in the warm skillet. Return the pan to the heat and let the berries cook until they begin to brown, 3 to 4 minutes.
If using lemon zest, stir it into the ricotta cheese.
Spoon the ricotta onto a serving dish and top with the roasted berries. Shower with the mint and serve the warm sauce on the side.