2 lbs. of carrots peeled and coarsely chopped
3-4 cups of seltzer
2 tbsp. unsalted butter
1 tsp. kosher salt
1 tbsp. chopped parsley (or another herb to give a different flavor)
In a large saucepan, put in the carrots and cover with the sparkling water. Bring to a boil, stir in the butter and salt. Reduce to medium heat and simmer for about 30 minutes. The seltzer should reduce about 3/4 and carrots should be really tender.
Transfer the whole thing to a food processor. Let it cool a bit before blending. Then blend until smooth. I let it go for a few minutes. Added in some more salt for taste and the parsley.
Voila. You can always add more butter to the process at the end but it isn’t necessary. It is really best served right after made. I put it in a saucepan and reheated before dinner. If you have to, it isn't the end of the world but it is definitely better to serve immediately and deal with the mess later.