Mix biscuit mix and water until a soft dough forms. If too sticky, add a little mix (up to 1/4 cup) until it handles easily. Knead gently on floured surface. Roll out to about 1/4 inch thick.
Spread butter over dough surface, then sprinkle 1/4 cup sugar over the top.
Roll up dough into a tight log and slice into 1/2 inch pieces.
Mix milk with vanilla and the other 1/4 cup sugar. Dip rolls in milk and place on baking sheet. Bake at 350F for about 25 minutes, or until golden on top.