Preheat the oven to 350˚F. Grease a 9-inch cake pan and line it with parchment paper.
Peel, core and slice the apples thinly. Toss them with the lemon juice and set aside.
Rub the grated lemon zest into the granulated sugar. Place the sugar in the bowl of a mixer. Add the butter. Beat together until the mixture is fluffy, scraping the bowl as needed.
Beat in the eggs one at a time. Then stir in the vanilla.
Fold in the flour and baking powder, alternating with the milk in two additions. Then fold in the apples and any lemon juice in the bottom of the bowl.
Scrape the batter into the prepared pan. Use a spatula to spread it out into an even layer. Run your index finger around the edge of the batter so that it doesn’t stick as the batter rises.
Scatter sliced almonds and some granulated sugar on top.
Bake until the cake has risen and is golden brown, for 40 to 45 minutes. Cool on a rack.