Apple Fritters with Orange Glaze

Whisk together flour, sugar, baking powder, and salt in a large bowl. In another bowl, whisk eggs, then whisk in milk, melted butter, zest, and vanilla. Add wet ingredients into dry and fold until just combined (do not overmix), then fold in apples. Heat 3/4 inch of oil in a 10- to 12-inch deep heavy skillet over medium heat until it shimmers. Drop a little batter into the oil. If it bubbles and rises to the top, the oil is ready. If it browns immediately, reduce heat. (Or use a deep-fat/candy thermometer to heat oil until it registers 375 °F.) Using two tablespoons (soup spoons), drop spoonfuls of batter, each containing 2 apple slices, into oil. Working in batches of 5, cook fritters, turning over halfway through, until golden brown, center is just cooked through, and apples are tender, 3 to 4 minutes total. Transfer with a slotted spoon to paper towels to drain. (Make sure oil returns to 375 °F between batches.)