Ingredients:

3/4 cup all-purpose flour
1 tsp baking powder
pinch of salt
1 extra large egg or 1 large egg plus 1 large egg yolk
3/4 cup sugar
1/2 tsp pure vanilla extract
1 stick (4 oz) unsalted butter, melted and cooled
1 to 1 1/2 apples, peeled, cored, and cut into 1/2-inch thick wedges

for glazing the cake
apple, quince or jelly preserves

Method:
Center a rack in the oven and preheat the oven to 350 ded F / 180 deg.

Whisk together the flour, baking powder and salt.

Working in a mixing bowl with the whisk, beat the egg and sugar together until thick and pale. Stir in the vanilla and then the melted butter. The mixture will be smooth and shiny. Stir in the dry ingredients and scrape the batter into the prepared pan. Top with the apples, making a spiral pattern. Leave some space between each slice, so the batter can puff up between the wedges - it looks much nicer with the puffs.

Slide the pan into the oven and bake for about 40 minutes, or until a knife inserted into the cake comes out clean. Transfer the cake to a cooling rack.

If you want to glaze the cake, warm a few spoonfuls of jelly/jam and a splash of water in a microwave oven (or a saucepan) until the jelly liquefies. Brush the jelly over the hot cake.

Let the cake cool for at least 15 minutes, or wait until it reaches room temperature, before you cut it into wedges to serve.