Prep the pan and air fryer. Use a 6-inch round cake pan or a small loaf pan that fits your air fryer basket. Grease it well and line the base with parchment. Preheat the air fryer to 320°F (160°C) for 3–5 minutes.

Cream butter and sugar. In a mixing bowl, beat the softened butter and granulated sugar for 2–3 minutes, until light and fluffy. This traps air and gives you a softer crumb.

Add eggs and flavor. Beat in the eggs one at a time. Stir in the lemon zest, vanilla (if using), and 1 tablespoon lemon juice. If it looks slightly curdled, don’t worry—flour will fix it.

Combine dry ingredients. In a separate bowl, whisk flour, baking powder, and a pinch of salt. Add half to the wet mixture, mix gently, then add the milk. Finish with the remaining flour, mixing just until combined. Don’t overmix.

Load the pan. Scrape the batter into the prepared pan, smoothing the top. Tap the pan gently on the counter to release air bubbles.

Bake in the air fryer. Place the pan in the basket. Cook at 320°F (160°C) for 28–34 minutes, or until the top is golden and a skewer comes out with a few moist crumbs. If the top browns too fast, tent loosely with foil during the last 8–10 minutes.

Make the lemon drizzle. While the cake cooks, whisk powdered sugar with 2–3 tablespoons lemon juice until smooth and pourable. You want it thick enough to cling, but not pasty. Add a splash of water if needed.

Pierce and soak. Let the cake cool in the pan for 10 minutes. Poke holes all over with a skewer. Spoon half the drizzle over the warm cake so it seeps in. Cool completely on a rack.

Finish with glaze. Once cool, spread or pour the remaining drizzle on top. It will set to a soft, glossy finish within 20–30 minutes.

Slice and serve. Cut into neat slices with a sharp knife. Wipe the blade between cuts for clean edges and a pretty glaze finish.