Heat the oven to 325°F and line 12 muffin cups with paper liners. Mix the almond flour, powdered allulose, salt, and melted butter, then divide the crumbs among the cups and press them down firmly.
Bake the crusts for 6 minutes. Let them cool while you prepare the cheesecake.
Beat the cream cheese and powdered allulose until smooth. Mix in the eggs one at a time, then blend in the sour cream and vanilla.
Divide the filling among the cups and bake for 17 to 20 minutes, until the edges are set and the centers still have a slight jiggle. Cool completely, then refrigerate for at least 2 hours.
Toast the chopped pecans in a dry skillet over medium-low heat for 3 to 4 minutes, stirring often, then transfer them to a plate.
Melt the butter in the skillet, stir in the allulose, and cook until light amber. Slowly stir in the warm heavy cream, then add the vanilla, salt, and toasted pecans and cook for 1 minute more.
Let the pecan topping cool until thick but spoonable, then mound it over the chilled cheesecake cups and serve.