Preheat the oven to 325°F (163°C) and line an 8x8 inch square metal baking pan with parchment paper, leaving an overhang on two sides.
In a medium mixing bowl, combine almond flour, powdered erythritol, and 1/4 teaspoon salt. Add melted butter and stir until a uniform, crumbly dough forms.
Press the dough firmly and evenly into the bottom of the prepared pan using a flat-bottomed measuring cup.
Bake the crust for 10 to 12 minutes until the edges are just beginning to turn a light golden brown. Remove from the oven and set aside.
In a medium saucepan over medium heat, melt 1/2 cup butter with the brown sugar substitute and allulose. Bring the mixture to a rolling boil.
Boil for 3 minutes, whisking constantly to prevent burning, until the mixture darkens slightly and thickens into a caramel consistency.
Remove from heat and immediately whisk in the heavy cream, vanilla extract, and flaky sea salt. Caution: the mixture will bubble vigorously.
Fold the chopped pecans into the caramel until thoroughly coated.
Pour the pecan mixture over the pre-baked crust and spread into an even layer using a heat-resistant spatula.
Return the pan to the oven and bake for 15 to 18 minutes, or until the filling is bubbling across the entire surface.
Allow the bars to cool completely in the pan at room temperature for approximately 1 hour, then transfer to the refrigerator for at least 2 hours to fully set the caramel before lifting out by the parchment and slicing into 16 squares.