Combine heavy cream, milk, and chocolate in the Instant Pot. Whisk gently.
Lock the lid into place and set the steam release handle (valve on top) to “Sealing”. Press Manual>Low Pressure>2 minutes.
When the Instant Pot has finished cooking, it will beep and switch to ”keep warm". Allow it to sit with the lid on for 5 minutes.
Slowly move the vent to "venting", testing to see if any milk comes through. If only steam is released, fully move the vent to venting and allow it to fully depressurize.
Stir in vanilla extract and serve.
Notes
There will be some natural separation in the cocoa. You can strain the mixture after cooking or whisk the mixture prior to serving.The cooking time remains the same even if you are doubling the recipe.Step 4 above is especially important for 3 and 6-quart models.