From Veg by HFW Serves 6

2 lbs Starchy Potatoes, peeled and cut into even-sized chunks
3 cups Whole Milk
14 oz Celeriac, peeled and cut into 1” chunks
3 TB Unsalted Butter, plus extra to taste
Sea Salt and freshly ground Black Pepper
A few gratings of Nutmeg

Add the potatoes to a large pot of salted water, bring to a low boil and cook until tender, about 20 minutes.  Drain well and leave to steam in a colander for a few minutes to drive off excess moisture.  While the potatoes are cooking, bring the milk to a boil in a separate saucepan.  Add the celeriac and simmer until very soft, about 20 minutes.  Drain, reserving the milk and keep it warm. Puree the celeriac in a food processor with the butter and about 2/3 cup of the hot milk.  Place the puree in a warmed large bowl. If you have a ricer or food mill press the potatoes through straight into the bowl with the celeriac, if not, mash them in a separate bowl until very smooth.  Using a wooden spoon, beat the celeriac puree with the potatoes until smooth and well combined, adding a little more of the hot milk and or some more butter until you get the consistency you like.  Season with salt, pepper, and nutmeg to taste and serve immediately.