Make the batter. Mix in a bowl flour, salt and pepper, then add slowly water and beer. Add the liquid little by little in order to avoid lumps. Let the batter rest in the fridge for half an hour until chilled.
Heat two inches of olive oil in a large skillet, dip the leaves into the batter and remove the excess. When the olive oil is hot, lay the leaves well spaced into the skillet and fry for a few minutes per side, until crisp, puffed and golden. Fry the leaves in batches, so they won't stick together.
Remove the sage leaves from the olive oil, lay them in a plate with a few sheets of paper towel to absorb the excess olive oil and sprinkle with sea salt. Enjoy!