To fill about 16, combine ricotta, mint, and lemon zest in a bowl. Season with kosher salt and freshly ground black pepper. Using a spoon, fill each blossom with about 1 Tbsp. ricotta mixture.
In a large pot, heat about 2" oil over medium heat until a deep-fry thermometer reads 350°. Combine flour and salt in a medium bowl, then whisk in beer until almost smooth (some small lumps are welcome—don't over whisk or you'll deflate the batter). One by one, dredge the blossoms in batter, shaking off the excess; gently lay them in the oil, without crowding the pan. Cook, flipping once with a slotted spoon, until golden brown, 2-3 minutes total. Transfer to paper towels to drain. Sprinkle with sea salt and serve while hot.