Make the lemon curd base: In a small saucepan, whisk 4 egg yolks, 1/2 cup granulated sweetener, 1/2 cup fresh lemon juice, 1 tablespoon lemon zest, and a pinch of salt. Cook over low to medium-low heat, whisking constantly, until thick enough to coat the back of a spoon, about 6–8 minutes. Remove from heat and whisk in 4 tablespoons butter, 1 tablespoon at a time, until glossy.

Cool the curd: Transfer the curd to a bowl. Press plastic wrap directly on the surface to prevent a skin. Let it cool to room temperature, then refrigerate until chilled, at least 45 minutes.

Whip the cream for the filling: In a chilled bowl, whip 1 cup heavy cream with 1 teaspoon vanilla and 1–2 tablespoons powdered sweetener until it reaches soft-to-medium peaks.

Fold into the curd: Gently fold the whipped cream into the chilled lemon curd until smooth and airy. This is your lemon cream layer.

Make the crust crumble: In a skillet over medium heat, melt 2 tablespoons butter. Add 1 cup almond flour, 1–2 tablespoons powdered sweetener, a pinch of salt, and a pinch of cinnamon if using. Stir frequently until golden and toasty, 3–5 minutes. Remove from heat and cool completely so it crisps up.

Whip the topping: Whip 3/4 cup heavy cream with 1 tablespoon powdered sweetener and 1/2 teaspoon vanilla to soft peaks.

Assemble the jars: Spoon 1–2 tablespoons of the almond crumble into each jar. Add a generous layer of lemon cream. Repeat layers if your jars are tall. Top with a swirl of whipped cream and a sprinkle of lemon zest.

Chill and serve: Refrigerate the jars for at least 30 minutes to set the layers. Serve chilled.