While your potatoes are boiling, prepare your creamy pilsner, mushroom sauce. In a large cast iron pan, add the olive oil. Preheat over medium, and add the mushrooms. Cook, stirring often, until the mushrooms are tender, about 6 minutes. Add the garlic and cook for an additional minute, or until fragrant. Add the pilsner beer, and bring it to a boil. Reduce heat and simmer for about 5 minutes or until the beer has reduced by about half. Add the green onions, Italian seasoning, crushed red pepper and a dash of salt and black pepper. Add the chicken broth and heavy cream. Bring to a heavy simmer and then reduce the heat to low. Cook for about 10 additional minutes, or until the sauce has reduced.