Sauté mushrooms and garlic in olive oil over medium heat until tender. Add Eliot Ness Amber Lager and cook until reduced by 1/4. Remove from heat. Add water to a sauce pot and bring to a boil. Add beef base to water and return to a boil. In a separate dish, mix flour and butter to create a well-mixed roux. Add mushrooms and garlic to water and boil. Mix in roux and allow to thicken. Stir out any lumps. Add salt and pepper to taste.