I make the spaetzle first. These can be made up to a day ahead and stored in the fridge. Mix all the ingredients except the heavy cream together in a bowl. Now thin the sticky dough into a batter that is a bit like really thick pancake batter with the heavy cream. I use a Spaetzle Maker to make my spaetzle, but you can either use a colander with wide holes or just flick the dough/batter off a cutting board with a knife.
Get a kettle of salty water going over high heat. Once it boils, make the spaetzle. Boil them hard until they float, then 1 minute more. Skim off with a slotted spoon or a spider skimmer. Move them to a baking sheet. When they are all made, toss them with a little oil so they don't stick together.
To make the stroganoff, salt the venison well and let it sit on the cutting board for 20 minutes or so. I do this while I make the spaetzle. Get 2 tablespoons butter in a large saute pan good and hot over medium-high heat. Pat the venison dry and sear all sides well in the butter. Cook it until it's rare to medium-rare. If you don't know how to determine this, use the finger test for doneness. When the meat is ready. move it to a cutting board and let it rest.
Add the mushrooms to the pan and turn the heat to high. Soon they will give up their water, and when they do, use a wooden spoon to scrape up any browned bits from the bottom of the pan. When most of the water has boiled away, add the rest of the butter to the pan along with the shallots and saute everything for 3 to 5 minutes, stirring often. Add the garlic, toss and cook over high heat for another 3 minutes or so. Sprinkle some salt over everything.
Add the Madeira and toss to combine. Let this boil down furiously. While it is doing so, grate some nutmeg over the mixture. When the Madeira is mostly gone, turn the heat down to low. Slice the venison thinly and return it and any juices that have collected on the cutting board to the pan. Stir to combine and add most of the chopped fresh dill.
Stir in the sour cream and turn off the heat. Stir to combine and let it heat through from the heat in the pan. Do not let this boil, or even simmer, or Very Bad Things will happen. Think nasty curdled crap. To serve, spread out over the spaetzle and top with any remaining dill and the dill pollen, if using.