In the bowl of an electric mixer, beat the softened butter with sugar and bourbon vanilla sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Mix together the amaranth flour, buckwheat flour, cream of tartar and salt and fold into the egg mixture. Stir in the milk until the batter is thick and smooth. Let rest 10 minutes.
Butter the waffle iron and prepare the waffles according to manufacturer's directions. Sprinkle the hot waffles with powdered sugar and serve as desired with fruit or berry compote and a dollop of whipped cream.