Combine the flour, nonfat dry milk, sugar, yeast, and salt in the bowl of a stand mixer fitted with the paddle attachment. Mix on low for 10 seconds.
Put the water and shortening in microwave-safe container and heat to 120 to 130ºF, approximately 2 minutes. Stir until the shortening is thoroughly melted. Add the water mixture to the dry ingredients and mix on medium speed until well combined, stopping to scrape down the bowl halfway through mixing, about 3 minutes. Cover the bowl with plastic wrap and refrigerate overnight.
The next morning, remove the dough from the refrigerator, uncover, and mix on medium speed for 3 minutes.
Position the 8 cans on a half-sheet pan and generously spray the rings and pan with nonstick spray. Sprinkle 1/2 teaspoon of oats in the bottom of each ring. Using a 2-ounce ice cream scoop or disher, scoop the dough into the rings, dividing it evenly between the rings. Sprinkle each top with 1/2 teaspoon of oats. Cover with parchment and let sit in a warm place for 60 minutes.
Heat oven to 400ºF.
Leave the parchment in place and set a second half-sheet pan on top. Bake for 20 minutes then remove the top half-sheet pan. Continue to bake until the muffins reach an internal temperature of 210ºF on an instant-read thermometer and are lightly browned, 5 to 10 minutes.
With the muffins still in the rings, remove the pan to a cooling rack for 10 minutes. Slide a knife around the perimeter of each ring to loosen. Set aside to cool completely.