Melt butter in a Dutch oven over medium heat. Add onions, leeks, 1 teaspoon of salt and 1/4 teaspoon pepper; sauté until soft and lightly browned. Add flour to pot and stir to coat onions/leeks. Cook for 2-3 minutes, stirring constantly, until you can no longer smell the flour.

Slowly deglaze the pot with beer, scraping the brown bits off the bottom of the pot with a wooden spoon. Allow beer to foam and cook for 2 minutes--this allows most of the alcohol to cook out. Stir in milk and vegetable stock. Season with mace, sugar, smoked paprika, and remaining salt and pepper. Combine seasonings and continue to cook until soup begins to thicken.

Stir in cheese; reduce heat to low. Simmer for 5-10 minutes, stirring occasionally. As soup simmers, make croutons.

Tear or cube rye or pumpernickel bread into one-inch cubes. Melt butter in sauté pan over medium high heat. When butter is melted, add bread. When bread is toasted on one side, flip to the other side until golden; remove to a paper-towel lined plate.

Once the soup thickens, it can be served as is, or it can be pureed. To purée, blend with a stick blender or purée in blender in batches to desired consistency. Serve immediately and garnish with croutons.