So apparently this isn't as odd-sounding as I thought at first blush, because everybody seemed pretty darn enthusiastic about it before even trying it. It's a sophisticated, somehow grownup-tasting soup (but don't let that stop you from trying it–my kids loved it. At least the older one loved it. The younger one ate everything except the Stilton garnish, to which he apparently objected on moral grounds.).
This soup reinforces the importance of garnishes, which I don't think I'd ever really used (other than the odd bit of parsley) before embarking on this project. Especially when the soup you're making is very uniform and smooth, garnishes add welcome contrast in color, flavor and–maybe most importantly–texture. I've learned to go ahead and make enough garnish for the whole pot of soup at the outset, because otherwise someone (Jim, at night… or me, at breakfast) ends up eating some unadorned soup in a fit of pure ravenousness, and it's just never quite the same without that crunchy/herby/creamy/bacony finish.
If you don't have croutons on hand (as I didn't), try cubing a couple slices of baguette or good rustic bread, tossing them with olive oil, salt and pepper, and baking them for about 20 minutes at 400 degrees until they're thoroughly dried out. Most soups allow enough simmering time that you can make the croutons while the soup's still cooking. (Bonus: they are about eight billion times better than any croutons you'll get from a store.) Or, if you don't have time/inclination to make croutons, try just toasting a couple pieces of bread, chopping them roughly and using them instead. Instant crouton fabulousness!
You'll need about half a pound of cheese for this soup, so plan accordingly.
Serves six (at least one person will want seconds)
3 Tbsp butter
2 small to medium onions, finely chopped
3 ribs celery, peeled with a vegetable peeler to remove coarse strings, finely chopped
1 medium head cauliflower, cored, broken or cut into 1" florets
6 cups chicken or vegetable broth
1-1/2 cups whole milk (or, as I did, about 3/4 cup each 2% milk and half-and-half)
Large pinch salt
1/2 cup half-and-half
About 2/3 cup crumbled blue Stilton
More salt & pepper
Croutons and additional crumbled Stilton, for garnish (probably the rest of the wedge of cheese)
In a soup pot, heat butter over medium-low heat. Add onions, celery and cauliflower and cook, stirring frequently, until onions and celery are tender, about 8 minutes. Add broth, milk and pinch of salt. Bring to a boil; cover, reduce heat, and simmer until cauliflower is super-duper tender, about 25 minutes. (Now would be a fine time to make the croutons, if that's how you're playing.)
Remove soup from heat. Puree in batches in a food processor or blender until very smooth. (An immersion blender, unless it's one of those Alton Brown-style industrial-strength ones, probably won't give you the velvety texture you're after here.) Return puree to pot and pot to stove.
Bring soup back to a simmer over medium heat. Reduce heat to low and whisk in half-and-half and Stilton, stirring constantly, until cheese is melted and soup is once again completely smooth. Don't let it boil. Taste and correct seasoning.
Serve promptly in shallow soup plates with croutons and Stilton arranged decoratively overtop.