Heat the olive oil in a large pot over medium heat. Stir in the onion, garlic, salt, and pepper. Cook and stir until the onion has softened and turned translucent, about 5 minutes. Stir in the beef, beer, sliced potatoes, and quartered potatoes. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until the beef is tender, about 2 hours. Season to taste with salt and pepper before serving.
