In a large bowl, whisk together the almond flour, sweetener, cocoa powder, and salt. Stir in the melted butter and vanilla extract until the dough comes together. If the dough is too crumbly to roll into balls, add water 1 tbsp at a time until it can be squeezed together. Roll into 1 inch balls and place on a waxed paper lined baking sheet. Freeze at least 1 hour. In a heatproof bowl set over a pan of barely simmering water, combine the chopped chocolate and the cocoa butter or coconut oil. Stir until melted and smooth. Drop a frozen truffle into the chocolate, tossing to coat thoroughly. Lift out with a fork and tap gently on the side of the bowl to remove excess chocolate. Return to the baking sheet to set. If using sprinkles to decorate, add them right away before the chocolate hardens. Repeat with remaining truffles.