Rinse and pat dry cherries and sage. Pluck off sage leaves.
Separate eggs. Stir flour and milk in a bowl until smooth. Mix in yolks, butter and lemon zest to form a thick batter. Let it rest for about 10 minutes.
Heat oil in a frying pan, a pot or a deep fryer until about 170°C (approximately 345°F).
Beat egg whites until stiff and sprinkle in sugar. Fold egg whites into batter.
Use tongs to dunk cherries and sage leaves into batter. Gently drop into oil and fry until golden brown, about 1 minute.
Remove, drain and let rest on a paper towel.
Sprinkle with powdered sugar and serve, as desired, with custard.