Clean blossoms. Remove pistil and stem of flowers, then rinse gently and dry on paper towel. (It's okay if they tear a little or open completely. It's easier to make sure there's no dirt or bugs inside.)
Make filling: In medium bowl, whisk together ricotta, basil, egg yolk and half Parmigiano-Reggiano. Set aside.
Make batter: Put flour and salt in a bowl to dip flowers into. Add milk, then water a little at a time. Beat with whisk or fork. Keep adding water until consistency is thick. Beat well another minute or two. Set aside to rest 10 minutes or longer.
Fill blossoms: With small spoon or piping bag, gently fill each blossom with 1-2 tsp filling and gently twist blossoms closed.
Dip & fry flowers: Preheat oil in frying pan. It should be hot when adding flowers. (Test it with a drop of batter if you're unsure.) Dip flowers into batter, coating well, then add to hot oil in pan. (You don't have to deep fry these. Pan frying in a little olive oil is just as good.) Fry until cooked on one side, then turn and continue to cook.
Remove and place on a wire rack over a paper towel lined pan. Best eaten while still hot/warm.
Remove and place on a wire rack over a paper towel lined pan. Best eaten while still hot/warm.