Chocolate Sauce Diabetic

1 tb Butter
2 tb Cocoa
1 tb Cornstarch
1 c Skim milk
1/2 ts Vanilla Artificial sweetener to equal 1/3 cup sugar

Mix all ingredients until well blended in suacepan. Cook over medium heat stirring constantly until slightly thickened. Remove from heat and set pan in ice water and stirl until completely cold. Sauce thickens as it cools. If not cooled over ice, the chocolate sauce will get a pudding-like skin and be rubbery.