Stir together milk, chocolate chips and corn syrup in a microwaveable bowl.
Microwave on HIGH (100%) for 1 to 2 minutes, stirring occasionally, until chocolate is melted. Add vanilla and cinnamon.
Serve over ice cream, pound cake or angel food cake. If not using immediately, refrigerate. Microwave chilled sauce 1 to 2 minutes, until sauce is warm and pourable.
Hot Fudge Mint Sauce: substitute peppermint extract for vanilla extract and omit cinnamon.
Warm Peanut Butter Sauce: substitute peanut butter chips for chocolate chips and omit cinnamon.
Milk Chocolate: substitue milk chocolate chips for semi-sweet, omit cinnamon.
White Chocolate: substitue white chocolate chips for the semi-sweet, omit vanilla and cinnamon. Add 1/2 teaspoon almond extract.
Orange: substitue dark chocolate chips for the semi-sweet, omit vanilla and cinnamon. Add 1/2 teaspoon orange extract.