Heat the oven to 400 degrees Fahrenheit and line a baking sheet with parchment paper. Lay out the broccoli in a single layer and drizzle with olive oil and salt and pepper. Bake for 20 minutes, or until tender, flipping once halfway through cooking. Set aside. Add the butter to a large pot on medium heat to melt. Add in the onion, celery, and carrot and sauté for 5-6 minutes or until cooked through and tender. Remove from the heat and place in a blender with the broth, Worcestershire, Dijon, black pepper, cayenne, and salt. Blend on high for 1 minute. Set aside 1 cup of the broccoli and add the remainder to the blender with the broth mixture. Blend on high to desired smoothness, around 1-2 minutes. Pour the mixture into the pot and pour in the lager. Heat over medium until it reaches a low simmer. While the mixture is heating, add both cheeses to a bowl with the flour and cornstarch and mix. Turn the heat to low and stir the half and half into the soup, cooking for 2-3 minutes. Whisk in the cheese, 1 cup at a time, until fully blended and smooth. Continue to cook, stirring occasionally, for 2-3 minutes until the soup thickens. If using a bread bowl, heat each bun whole according to the directions. Once warm, scoop out the middle to form a bowl. Ladle the warm soup into the pretzel bowl and top with reserved broccoli. Serve and enjoy!