Step 1

Heat oil in a large Dutch oven over medium heat. Add onion, bell pepper and serranos; cook, stirring occasionally, until the vegetables are tender and slightly browned, 8 to 10 minutes.

Step 2

Add flour; cook, stirring often, until the vegetables are coated, about 1 minute. Slowly stir in beer; cook, stirring constantly and scraping the bottom of the pot with a wooden spoon in figure-8 motions, until thickened, about 1 minute.

Step 3

Add broth, half-and-half and mustard, stirring until combined. Bring the mixture to a boil over high heat. Reduce heat to low; simmer, stirring occasionally, until thickened, 4 to 5 minutes. Remove from heat. Whisk in cheese, pepper, salt and cayenne until melted and combined, about 1 minute. Working in batches, pour the mixture into a blender. Secure the lid on the blender and remove the center piece to allow steam to escape. Place a clean towel over the opening. Process until pureed to desired consistency, 1 to 2 minutes. (Use caution when blending hot liquids.) Ladle the soup into 6 bowls. Top with bacon, scallions and/or chives, if desired.