Whisk in milk, then cognac and a pinch of salt. Heat dry skillet over moderately high heat until hot. Peel wrapper back slightly from butter and rub enough over bottom of skillet to lightly coat. Pour about 1 tablespoons batter into skillet, tilting to coat bottom. Cook until just cooked through, about 20 seconds.
Transfer crepe to a plate and fold into quarters.
Make 5 more crepes in same manner with about half of remaining butter and all of remaining batter. Saute crepes until golden, about 30 seconds, then invert onto a plate. Serve crepes sprinkled with sugar. Garnish with strawberries, if desired. Makes 2 servings.