Char the poblanos. Before making the sauce, we want to char the poblanos for flavor and so they're nice and soft. Use a pair of tongs and rotate them over the flame on a gas burner until they're blackened all over. Alternately, place them on a baking sheet and broil on high heat, turning the peppers once, until blistered all over. Place the hot charred peppers in a ziplock bag or a heat safe bowl and cover with plastic wrap. Once the peppers are cool, peel and dice them, discarding the seeds and stem.
Make the sauce. Combine the diced poblanos and the remaining sauce ingredients in a blender and blend until smooth. If you need to thin the sauce a bit, just add a touch more water or broth. Season to taste with salt and pepper. Set aside.
Preheat an oven to 375 F.
Make the filling. Heat the oil in a large skillet and add the onions. Saute for 2-3 minutes until soft and then add the ground beef. Use a silicone spoon or spatula to break the meat up as it cooks. Add the taco seasoning, diced potatoes, and corn and stir well to combine. Cover and cook for 10 minutes, or until the potatoes are soft. Season to taste with salt and pepper. Remove from the heat and cool for 15-20 min. The filling can be made up to 5 days in advance.
Prepare the baking dish. Lightly spray a 9x13 baking dish with nonstick spray. Pour a thin layer of the sauce on the bottom of the dish.
Roll the enchiladas. Microwave the flour tortillas for a few seconds so that they're pliable. Place about 1/3 cup of the filling on the tortilla and top with some shredded cheese. Use about 2 cups of cheese between all the enchiladas, leaving 1/2 cup for topping. Roll it up and place it seam side down in the baking dish. Repeat with the remaining filling and tortillas.
Top and bake. Pour the rest of the sauce over the enchiladas and top with the remaining shredded cheese. Bake uncovered until for 30-35 minutes until hot and bubbly. Remove from the oven and top as desired.