Place the bacon strips in a dutch oven casserole pot and turn the heat on to medium, allowing the meat to heat up at the same rate as the pot, rendering the fat nicely.
Once the bacon is crispy, remove it to a plate using a slotted spoon.
Add more butter to the pot, and then the onions.
Cook the onion in the butter and bacon fat, and once they are softened, add the flour, whisking it into the butter to avoid lumps.
Pour in the beer, whisking all the while, and then bring to a simmer and leave for five minutes to cook off the alcohol.
Stir through the chicken broth, and then the mustard and cayenne pepper. Allow the flavours to incorporate for a further five minutes.
Now add the cream, and once it is back at the simmering point, turn off the heat.
Gradually add the grated cheddar cheese, allowing it to melt and incorporate into the soup. Once all the cheese is added, turn the heat back on and gently bring back up the temperature but do not allow it to boil.
Warm your pretzels or bread in the oven and serve the soup in bowls topped with bacon and spring onion.