Line an 8-inch square baking pan with either parchment paper or aluminum foil. Lightly spray with oil spray and set aside. Make sure the foil or parchment drapes over the side so you can pick it up later.
Combine the sweetened condensed milk and the chocolate chips in a microwave-safe bowl, and microwave for about two minutes, stirring occasionally until melted, smooth, and fully combined.
Pour the chocolate mixture into the prepared pan.
Chill for at least two hours.
Remove from the pan, slice into pieces, and serve.