Preheat oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper.
In a large bowl, whisk together the almond flour, erythritol, and salt. Add the cold cubed butter and cut it in using a pastry cutter or your fingers until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
Add the egg and stir until the mixture just comes together into a crumbly dough. Set aside about 3/4 cup of the mixture for the crumble topping. Press the remaining dough firmly and evenly into the bottom of the prepared pan.
In a bowl, toss the diced strawberries with the erythritol, lemon juice, vanilla extract, and xanthan gum. Let it sit for 5 minutes so the strawberries release a bit of juice and the xanthan gum thickens the mixture slightly.
Spread the strawberry filling evenly over the pressed crust. Scatter the reserved crumble mixture over the top, breaking up any large clumps with your fingers.
Bake for 30 to 35 minutes, until the crumble topping is golden brown and the strawberry filling is bubbling around the edges.
Let the bars cool completely in the pan before slicing. For the cleanest cuts, refrigerate for at least 1 hour before cutting into 12 bars.
