Place the celeriac on your work surface with the cut root end down. If it doesn't feel stable slice a bit more off the bottom to give you a nice firm base. Slice the root into 1/2 inch thick slices, then dice 1/2 inch cubes. A mandoline makes quick work of this.
Heat the olive oil in a heavy bottomed stock pot or dutch oven over medium-high heat. Once the oil starts to shimmer add the celeriac, thyme and garlic. Season with salt and pepper and stir for 5 minutes.
Reduce the heat down to a simmer and add the stock. Lid the pot and cook for an additional 25 minutes, or until tender.
Mash the celeriac using a potato masher or wooden spoon. A potato ricer can be used but it will need to be cleaned out between presses. Leaving some cubes in the mix helps give a more diverse texture. If you desire a silky mash you can process it in a food processor, just a add a bit of dairy or other liquid.
Enjoy, pairs especially well with grilled and roasted meats.
