Preheat oven to 350°F (175°C). Grease an 8-inch baking pan or line with parchment paper.
In a mixing bowl, combine almond flour, baking powder, salt, and cinnamon (if using).
In another bowl, whisk eggs, honey (or sugar), and vanilla extract until smooth.
Fold the wet ingredients into the dry ingredients until a uniform batter forms.
Pour the batter into the prepared pan and spread evenly.
Arrange thin apple slices on top in a single layer.
Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool for 10 minutes before slicing. Serve warm or at room temperature.