Pre-heat the oven to 325 degrees. Warm the olive oil in a large skillet over medium-low heat. Add the garlic and onions and cook until the onions are tender (about 4 minutes). Add the mushrooms and saute until the mushrooms are tender and beginning to brown, stirring occasionally. Remove the onions and mushrooms and set aside. Melt the butter in the pan and add the flour, stirring to avoid lumps. Return the mushrooms and onions to the skillet and stir them around to coat with butter and flour. Place the mushroom and onion mixture in a casserole dish with a cover, crack open the bottle of beer, and pour it over the mushrooms and onions. Season with salt and pepper, cover, and bake in the oven for 1 hour 15 minutes. Remove the lid of the casserole and continue to cook for another 15 minutes, uncovered. In the meantime, bring a large pot of water to boil. Steam the kale over the boiling water until tender, about 3-4 minutes. Place the kale aside, and cook the pasta (in the kale water) according to package directions. To serve, place a portion of pasta on each dish, top with steamed kale, and ladle the mushrooms and beer over everything. Season to taste with salt and pepper, and garnish with fresh parsley, if desired.