Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan with butter or oil. Line the bottom with parchment paper for easy removal after baking.
In a large bowl, whisk together ricotta cheese, eggs, honey (or maple syrup), lemon zest, lemon juice, and vanilla extract until smooth and creamy. If the mixture looks slightly curdled, keep whisking—it will come together.
In a separate bowl, mix almond flour, baking powder, and salt. Stir well to evenly distribute the baking powder.
Add the dry mixture to the wet ingredients. Use a rubber spatula or spoon to gently fold until just combined and no dry spots remain. Avoid overmixing.
Pour the batter into the prepared pan. Smooth the top with a spatula. Add sliced almonds on top if desired.
Bake for 35–40 minutes, until golden brown, the edges pull slightly from the pan, and a toothpick comes out clean or with a few moist crumbs.
Let the cake cool in the pan for 10 minutes. Then transfer to a wire rack to cool completely. Finish with a dusting of powdered sugar or a drizzle of honey before serving.