Arrange a rack in the upper third of the oven and preheat the oven to 450°F.
Heat a large skillet over medium-high heat and add the oil. Add the shallots and a pinch of salt and cook, stirring, until softened, 5 to 7 minutes. Add the ground beef and season it with 1 teaspoon salt. Brown the beef, breaking it up with a wooden spoon or spatula. Stir in the green beans and cook for a few minutes, until thawed. Use a slotted spoon to transfer the mixture to a 9 x 13-inch casserole dish and spread it out evenly. Set aside while you make the creamed soup.
Discard the juices that remain in the skillet, wipe it out, and return to medium heat. Melt the butter and whisk in the flour to make a paste. Cook, whisking, for 2 minutes. Whisk in the pale ale, then add the chicken stock very gradually, in 3 or 4 additions, whisking continuously and allowing the mixture to thicken before each addition. Whisk in the heavy cream, a bunch of turns of black pepper, the thyme, and the nutmeg. Increase the heat and continue whisking frequently until it just begins to simmer, then reduce the heat to low and simmer very gently for 5 minutes, whisking occasionally. Taste and adjust the seasoning as desired. Pour or ladle the mixture all over the ground beef and fold together to incorporate. Top with perfectly aligned rows and columns of Tater Tots (adding a layer of cheese under or over the tots, if desired) and season with salt and pepper.
Bake until the tots are golden brown and crispy on top; begin checking for doneness at 35 minutes (or a few minutes earlier if you have cheese on top). If you want to get the tots even crispier, finish with a few minutes under the broiler. Let cool slightly, top with parsley, and/or serve with ketchup, if desired.
TO MAKE AHEAD: Complete the steps up through topping with tots (and cheese, if using), assembling in a 9 x 13-inch metal casserole dish. Let cool, wrap in plastic or foil, and refrigerate or freeze until ready to cook. It'll last 2 days in the refrigerator and 3 months in the freezer. If reheating from the fridge, proceed as directed, but add on a few more minutes in the oven to ensure that it's heated through. To reheat from frozen, cover loosely with foil and bake at 350°F for an hour, then uncover, increase the heat to 450°F, and bake until the tots are golden brown and the innards are heated through; begin checking for doneness at 20 minutes. Let cool slightly, top with parsley, and/or serve with ketchup, if desired.
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