Trim the zucchini blossoms of their green base, then let the stamens drop out from inside the blossoms. Cut the trimmed blossoms into strips.
In a large mixing bowl, mash the ricotta up until soft, then add the grated cheese, eggs, flour and salt. Mix together, then whisk in enough milk so you wind up with a smooth, pourable but not runny batter. Fold in the cut up blossoms so they are completely covered in batter. Let rest at least 15 minutes.
In a large skillet, heat enough olive oil about 1cm (3/8 inch) deep until hot but not smoking. Add dollops of the batter by heaping spoonfuls into the oil and fry until cooked through and golden brown, about 2 minutes on each side.
Once done, drain the frittelle on paper towels. Serve while still warm.