Stir the rhubarb, sugar, and lemon juice together in a small bowl. Set aside until soft and juicy, about 1 hour.
Puree the rhubarb and frozen strawberries, ice cream, vodka, and Cognac in a blender until smooth and pink. Pour into a chilled brandy snifter or parfait glass. Garnish with a strawberry or rhubarb strip. Serve with a thick straw or sundae spoon. Drink.