Place the ice cream maker core (freezer bowl) in the freezer the night before to ensure it’s fully frozen and ready for churning.
Measure the milk and heavy cream into a liquid measuring cup. Pour the mixture into a small saucepan and heat over medium-high until it just begins to simmer.
While heating the cream, combine the maple syrup (or your preferred sweetener), sea salt, and egg yolks in a liquid measuring cup. Whisk them together until smooth.
Once the milk reaches a gentle simmer, slowly pour in the egg yolk mixture while whisking constantly to prevent the eggs from scrambling. Continue cooking for 2–3 minutes, whisking often, until the custard thickens slightly and coats the back of a spoon.
Pour the custard into a liquid measuring cup or glass bowl and let it cool completely. Once cooled, whisk in any flavorings like vanilla or extracts. Cover and refrigerate overnight for the best results.
Before churning, prepare your mix-ins so they’re ready to fold into the ice cream at the right time.
Use a milk frother to blend a scoop of protein powder into the chilled custard until smooth. Then, set up your ice cream machine and pour the custard in to begin churning.
Once the ice cream starts to thicken and become creamy in the machine, add your prepared mix-ins and let it churn just until evenly combined.
Scrape the soft-serve ice cream from the machine into a pint-sized glass container. Smooth the top, cover with a lid, and freeze for at least 5 hours to set fully. Then enjoy!
