In a medium-sized bowl, combine heavy cream, whole milk, mint extract, and granulated sugar. Whisk until smooth and all sugar granules dissolve, about 1-2 minutes.

Cover with plastic wrap and refrigerate overnight for at least 8 hours to meld flavors and increase creaminess.

Pour the chilled mixture into the Ninja Creami container. Process according to instructions (typically 3-5 minutes) until creamy.

Remove the container and gently fold in the chocolate chips using a spatula.

Serve immediately for a soft-serve texture or freeze for a firmer consistency. Let sit at room temperature for 5-10 minutes before serving.