Substitute to grain mustard I am planning on doing a recipe of mustard sauce pork. Here is the recipe for the sauce (quantities are approximate, the recipe is inspired from a Gordon Ramsay Youtube video):

Ingredients


1 tbsp vegetable oil
1 tbsp garlic
1 tbsp chopped shallots
calvados
chicken stock
cooking cream
1 tbsp dijon mustard
1 tbsp grain mustard


Method


In hot pan, caramelize garlic and shallots.
deglaze with calvados, flambée if possible and reduce.
Add about 1 1/2 cup of chicken stock and reduce by half.
Add cream for richness and thickness, bring to a boil.
Add mustards and let simmer for 5-10 minutes to meet desired consistancy.


This previous is the sauce of a more complete recipe but it does not depend on the rest of the dish to be a fine sauce, asides from the pork residue in the pan for taste.

Now the problem is, I don't have any grain mustard, but have mustard seeds at home as well as regular Dijon mustard.

Would it be possible to substitute the grain mustard by the same quantity of regular Dijon plus mustard seeds without compromising the taste too severely?
Yes, add the mustard seeds to the Dijon mustard and add a splash of vinegar, stir well and let it sit like that for 24h.

For the impatient / I don't have 24h  ;-)

Microwave the newly created mixture for one minute @ 750W (without the metal lid on!) and stir again after microwaving. (Use oven mittens!)