Prep the pan and oven: Preheat the oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment, leaving overhang for easy lifting. Lightly grease the sides.

Make the crust: In a bowl, stir together 2 cups almond flour, 1/3 cup granulated keto sweetener, a pinch of salt, 1 teaspoon vanilla, and 1/2 cup melted butter. Mix until it looks like damp sand and holds together when pressed.

Press and par-bake: Press the crust firmly and evenly into the lined pan. Dock with a fork a few times to prevent bubbling. Bake 12–15 minutes, until lightly golden at the edges. Set aside to cool slightly.

Whisk the filling: In a medium bowl, whisk 3 large eggs + 2 egg yolks with 2/3 to 3/4 cup powdered keto sweetener, 1/4 cup fresh lemon juice, 1 tablespoon lemon zest, 1 teaspoon vanilla, and a pinch of salt. Sprinkle in 2 tablespoons almond flour (or 1 tablespoon coconut flour) and whisk smooth. Slowly stream in 3 tablespoons melted butter while whisking.

Taste and adjust: Dip a clean spoon in and taste. Add a touch more sweetener or lemon juice to balance the tartness. It should be bright but not harsh.

Pour and bake: Pour the filling over the warm crust. Reduce oven temp to 325°F (165°C). Bake 16–22 minutes, until the center just barely jiggles and the edges are set. Do not overbake—carryover heat will finish it.

Cool and chill: Cool in the pan on a rack for 1 hour, then chill at least 2 hours (overnight is even better). This helps the bars slice cleanly and the lemon flavor bloom.

Slice and serve: Use the parchment to lift out. Dust with powdered keto sweetener if you like, then cut into 16 small or 9 larger squares. Serve chilled or at cool room temp.