Prepare potato topping: In a large saucepan add the potatoes and garlic and cover with cold water. Bring to a boil over medium heat and cook, uncovered, until the potatoes are fork-tender, about 15 to 20 minutes. Drain. Transfer the potatoes and garlic to a large bowl. Add the sour cream, 1/4 cup of the broth, butter, salt and pepper, and beat on low speed with a hand mixer until the potatoes are light and fluffy, about 1 to 2 minutes. If the mixture is too dry, add the remaining 1/4 cup broth. Do not overmix. Cover and set aside.
Preheat the oven to 350 degrees F. Spray a 10-inch round baking dish with nonstick spray.
Prepare filling: Heat a large skillet over medium heat. Add the bacon and cook, stirring occasionally until browned and almost crisp, about 7 to 8 minutes. With a slotted spoon, transfer the bacon to a plate; set aside.
Add the oil to the drippings in the skillet and put over medium heat. Add the onions and 1/2 teaspoon of salt, and cook, stirring occasionally, until the onions are very soft and just beginning to brown, about 10 minutes. Sprinkle in the sugar, and cook, stirring occasionally, until the onions begin to caramelize, about 3 minutes. Stir in the beef and cook, stirring occasionally, over medium-high heat, until the beef begins to brown, about 7 minutes. Add the carrots, peas, and garlic and cook, stirring, until the vegetables begin to soften, about 5 minutes. Stir in the tomato paste and flour and cook, stirring, until well blended, about 2 minutes. Add the beer, bring to a boil and boil for 3 minutes. Cook, stirring with a wooden spoon, and scraping up the browned bits from the bottom of the pan, about 2 minutes Add the cooked bacon, the broth, rosemary, 1/2 teaspoon of salt, and the pepper, and bring to a boil. Reduce the heat and simmer, uncovered, until the sauce thickens, about 15 minutes.
Spoon the meat mixture into the prepared baking dish. Spread the potato topping evenly over the beef mixture. Bake until the filling is hot, the topping is lightly browned and the edges are bubbly, about 35 minutes. Remove from the oven and sprinkle with the cheese. Return to the oven and bake for 10 more minutes. Let rest out of the oven for 10 minutes before serving. Sprinkle with parsley and serve.