Step 1

In a heavy-bottomed saucepan, whisk together egg yolks, sugar, corn syrup, and cocoa powder until well combined. Whisk in cream and milk until yolk mixture is fully incorporated.

Step 2

Place pot over medium-low heat and cook, whisking frequently, until a custard forms on a spoon and a finger swiped across the back leaves a clean line, or until custard temperature reaches 170°F. Stir in salt and vanilla.

Step 3

Strain custard through a fine mesh strainer and chill in either ice bath or refrigerator until it is very cold, about 40°F. Churn in ice cream maker according to manufacturer's instructions, then serve right away or transfer to an airtight container and chill in freezer for 1 hour to let custard firm up slightly. Serve custard within two hours of it being made.

Step 4

Optional: To make concrete-style drinks, finely chop up ingredients like M&M's, heath bars, cookies, or pretzels and store in freezer, then add to ice cream machine during last two minutes of churning. Serve right away in a glass or cup with a straw and a long spoon.