Heat the oven to 350°F (175°C). Lightly grease three 6-inch round cake pans or two 8-inch round cake pans with nonstick baking spray. Place a parchment-paper round in the bottom of each pan, then set the prepared pans aside.
In a medium bowl, whisk together the blanched almond flour, coconut flour, baking powder, baking soda, and sea salt until evenly distributed.
Stir the room-temperature almond milk together with the vinegar in a separate measuring cup. Allow the mixture to stand for approximately 5 minutes, giving it time to curdle slightly and form a quick dairy-free buttermilk-style mixture.
In a large bowl, whisk the room-temperature eggs with the granulated monk fruit sweetener, cooled melted coconut oil, vanilla extract, lemon extract, lemon juice, and grated lemon peel. Add the curdled almond milk mixture and stir until thoroughly incorporated.
Gradually add the dry mixture to the wet ingredients. Stir only until the ingredients are combined and the batter becomes smooth, taking care not to overmix.
Distribute the batter evenly among the prepared cake pans and level the surfaces with a spatula. Bake for 19–24 minutes, or until a toothpick inserted into the center of a cake layer comes out clean.
Leave the baked cakes in their pans for at least 30 minutes. Carefully release them from the pans afterward and place them on wire cooling racks. Allow the layers to cool completely to room temperature before frosting.
Add the softened cream cheese to the whipped butter and continue beating for another 3 minutes, until the two are fully blended.
Gradually incorporate the powdered monk fruit sweetener, vanilla extract, lemon extract, finely grated lemon zest, and almond milk. Beat for another 2–3 minutes, until the frosting has a creamy, smooth consistency. Cover and refrigerate until needed.
Set one completely cooled cake layer on a serving platter or cake stand. Spread an even layer of lemon cream cheese frosting over the top. Add the next cake layer and repeat the process until all layers have been stacked with frosting between them.
Use the remaining frosting to cover the sides of the cake if a fully frosted finish is desired. Arrange fresh lemon slices over the top for decoration.
Refrigerate the assembled cake for 1–2 hours before cutting. This resting period allows the frosting to firm slightly and helps the cake slice more neatly.