Reddit reviews Plochman's Premium Natural Stone Ground Mustard, 20.5 Ounce (Pack of 12)

Don't know about that recipe, but here's our instant-pot-ized recipe:

Get two carrots, an onion, an amount of garlic that you would consider a good amount of garlic (we use a head), a bay leaf, some peppercorns, maybe a clove, an apple if you're feeling fancy. Chop the big stuff in half or in quarters, toss it in the pot along with a half-cup of water to get the pressure thing started. Instant-pot on high pressure for 50 minutes.

Here's the second part that is delicious and that can be done with either recipe:

Heat oven to 350. Mix two tablespoons brown sugar and two tablespoons stoneground mustard (we use Plochmann's). Put the corned beef on a pan, glaze the top of the corned beef with the sugar/mustard mix, put it in the oven for 15 to 20 minutes - it should form a nice glaze. (Don't let it burn.)