An Upper Midwest classic, this recipe works with any meat, not just venison, and you can either use canned cream of mushroom soup, or make your own, which is easy.
Brown the ground venison in a large pan; use a little oil if the grind has no extra fat. After it has mostly browned, add the celery and chopped onions and keep cooking until the meat is nicely browned and the onions are soft, about 8 minutes.
Meanwhile, bring a medium pot of water to a boil and add the dried mushrooms. Turn off the heat and let them soak.
Add the chopped garlic and some salt to the pan with the meat and onions. Cook this over medium-low heat for about 2 minutes, stirring well.
Fish out the mushrooms, squeeze them to remove excess moisture and chop roughly. If the soaking water is full of debris, strain it. If not, pour about 1/3 into the pan with the meat and onions. Bring this to a boil.
Add half the marjoram and mustard to the meat mixture and boil this down until it's mostly dry.
While this is happening, preheat the oven to 350°F. Put the mushrooms, another 1/3 of the soaking water, the other half of the marjoram, a pinch of salt and black pepper, and the cream into a blender and puree. If it's too thick, add a little more soaking water. Taste it and add more salt if need be. Pour this into the pan with the meat, add the peas and stir well.
Pour all this into a casserole dish; a typical 9x13" works well. Spread it evenly. Add a layer of grated cheese over everything, as thick as you want. Then arrange tater tots to cover it all, pressing in a little. Bake for 45 minutes uncovered.
Take it out of the oven, let it cool a bit before serving, ans sprinkle with parsley, if using.
Notes
If you don't want to make your own cream of mushroom soup, simply use 1 or 2 cans of the stuff. I don't love it, but many do.