Combine agave syrup with 2 tbsp water and vanilla in a small saucepan and set
over medium-high. Bring to a boil, then remove from heat.
Beat egg whites with cream of tartar on high in the bowl of a stand mixer, until soft peaks form when beaters are lifted, about 1 min. Slowly pour hot syrup in a stream down the side of the bowl, beating until stiff peaks form, 2 to 3 more min. Frosting should hold its airy texture. Spread or pipe frosting on Super-Awesome Chocolate Muffins. Sprinkle with grated chocolate.