1 Large celery root approximately 1 1/2 pounds
3 1/2 Pounds peeled Yukon gold potatoes
2 Tablespoon + 1 teaspoon salt
2 Cups heavy cream
3/4 Cup water
1 Bay leaf
4 Sprigs fresh thyme
2 Tablespoon butter at room temp
Salt and ground white pepper to taste
Celery root is a good way to add a bit more flavor and depth to mashed potatoes. If you want a more rustic side dish, use red potatoes and smash them with the skin on.
Peel the potatoes and cut in to large pieces being careful to keep them similar in size so they cook in the same amount of time.
Place cut potatoes in pot with 2 tablespoon of kosher salt and enough cold water to cover them by an inch.
Bring to a boil and then turn them down to a simmer with the water just barely moving (cooking at a low enough temp that the potatoes maintain shape and are barely moving). Test a piece by inserting a knife to check doneness.
Once they are finished, pour into a strainer to drain off water. While potatoes are cooking, wash the celery root and cut off each end. Peel the remaining outer layer with your knife. Cut into 1-inch square pieces and place in pot with bay leaf, thyme, 1 teaspoon salt, 2 cups heavy cream and 3/4 cup of water.
Slowly bring the celery root up to a simmer and keep heat low until there is no resistance when inserting a knife.
Make sure your temperature is not up too high, otherwise you will over reduce the cream. When celery root is done, carefully remove thyme and bay leaf.
Transfer celery root and cream mixture to a blender and puree until smooth. Using a potato ricer, process the potatoes.
You can use an electric mixer but mix as little as possible to avoid potatoes becoming too starchy.
Fold the butter and cream mixture into the potatoes and season with salt and ground white pepper.