Melt the butter in a Dutch oven or large saucepot over medium heat. Add the carrots, celery, garlic, onions, mustard powder, cayenne and sprinkle with salt and pepper. Sweat the vegetables until tender, about 15 minutes. Sprinkle the flour over the vegetables and cook, stirring constantly, about 1 minute. Pour in the stock, mustard and Worcestershire and simmer until the veggies are very soft, about 15 minutes. Add the ale, simmer, about 5 minutes, and then puree with an immersion blender until smooth. Add the Cheddar, gruyere and half-and-half and stir until melted through and smooth. Adjust the seasoning and top with the Garlic Butter Crostini. Enjoy with a 30-pack of your favorite cheap beer.
Heat a grill pan over medium heat. Brush the baguette slices on both sides with the butter and sprinkle with salt. Grill the slices on both sides until grill marks form, about 3 minutes per side. Rub the slices with the garlic.