In a medium saucepan, gently melt the butter, brown sugar replacement, and allulose over medium heat. Bring the mixture to a boil and let it cook for just 2 to 3 minutes, stirring occasionally, being careful not to let it burn. Take it off the heat and carefully stir in the heavy cream – it will bubble! Set it aside to cool down until it's just lukewarm.
Grab your food processor and finely chop the toasted pecans. You want them to be like coarse crumbs with a few slightly bigger pieces for a nice bite. Set aside about 3 tablespoons of these chopped pecans for decorating later. Transfer the rest to a large mixing bowl.
To the bowl with the pecans, add the almond flour, powdered sweetener, and salt. Give it a good stir to combine everything. Pour in your lukewarm caramel sauce and mix it well until the dough starts to clump together and holds its shape.
Scoop out about 1 tablespoon of dough at a time. Press it firmly with your hands and then roll it into a neat little ball. Place all your truffle balls on a cookie sheet lined with waxed paper. Pop them into the freezer for about 1 hour to let them firm up nicely.
Create a makeshift double boiler: place a heatproof bowl over a pan of barely simmering water (make sure the bowl doesn't touch the water). Add the chopped sugar-free dark chocolate and cocoa butter to the bowl. Stir gently until it's all melted and wonderfully smooth.
Take one firm truffle ball and dip it into the melted chocolate, making sure it's fully coated. Lift it out with a fork and gently tap it against the bowl's edge to shake off any extra chocolate. Quickly sprinkle a little of your reserved chopped pecans onto the top of each truffle before the chocolate sets.
Place the decorated truffles back on the waxed paper and refrigerate them until the chocolate coating is completely firm.