For a quick and easy hot fudge sauce, melt one stick of butter (1/2 cup), in a saucepan over medium heat. When the butter is melted, add 1 cup chocolate chips, and stir them in until melted. Add 14 ounces of sweetened condensed milk, and stir.
This is a great sauce to serve over ice cream. Any amount left over can be refrigerated.
For a richer sauce that is still simple to make, simply add a few ingredients and steps. In a saucepan over medium-high heat, bring 2/3 cup heavy cream, 1/2 cup light corn syrup, 1/3 cup brown sugar, 1/4 cup Dutch-processed cocoa powder, 1/4 teaspoon sea salt and 3 ounces chopped bittersweet chocolate to a boil. Bring down the heat to low, and simmer for five minutes, stirring as needed. Turn off the heat, and stir in 3 more ounces chopped bittersweet chocolate, 2 tablespoons unsalted butter and 1 teaspoon vanilla extract, and continue stirring until the sauce is smooth and silky. Let the sauce sit for half an hour. The sauce thickens as it cools. Serve the sauce over your favorite ice cream or dessert. It can also be stored in a jar in the refrigerator for up to two weeks.