Years ago, I made this for my mom on a Sunday in January. She wasn’t feeling well and asked for something that was “easy on the stomach.” That meant no onions. I couldn’t fathom soup without onions. I surprised myself by coming up with something that was wonderful—so good that I wrote down the recipe! The parsnips give the soup a slightly sweet flavor that is rather seductive. Once cooked, the potatoes and the parsnips look the same, so it is hard to place the flavor…it’s just good!
Melt the butter over medium heat. Turn the heat to medium-high and sauté the celery, carrots, and parsnips for a few minutes. Add the thyme, mustard seed, celery seed, and bay leaf, then turn the heat down and cover and sweat the veggies until the celery is translucent and the veggies are slightly softened.
Add the diced potatoes, the stock, and the water. Turn the heat up to high and stir in the broth. Bring to a boil, then turn down the heat, cover it and cook until the potatoes are done, about 8 minutes.
Remove the bay leaf and discard.
Remove about 2 cups of soup from the pot to a blender. Add the half and half and the flour and blend well. Return to the pot and add salt and pepper to taste. (I often do not add any additional salt.) Simmer and stir until thickened, about five to seven minutes.
For a creamy, blended soup, blend in batches with the half and half until smooth and creamy. Do not add flour. Return to the pot and reheat until hot.