Preheat your oven to 350°F (175°C).
Peel and slice the apples, then toss them in a bowl with lemon juice and a pinch of cinnamon.
Spread the apples evenly in a greased 9x9-inch baking dish.
In another bowl, mix together the almond flour, erythritol, cinnamon, and salt.
Pour in the melted butter and vanilla extract, then stir until the mixture is crumbly.
Sprinkle the almond flour mixture over the apples, ensuring even coverage.
Bake for 35–45 minutes or until the topping is golden brown, and the apples are tender when pierced with a fork. Adjust the baking time depending on the thickness of your apple mixture.
Let the apple crisp cool for 10 minutes before serving.
Serve warm with a scoop of keto vanilla ice cream or a slice of banana bread donut.
Garnish with extra cinnamon or nuts if desired.