Preheat the oven to 350°. In a small saucepan, cover the garlic with the oil and simmer over low heat until the garlic is tender, about 12 minutes. Let the garlic stand in the oil.
Using a sharp knife, peel the celery root and cut into 1-inch cubes. In a saucepan, cover the celery root with water and bring to a boil. Add a large pinch of salt and simmer over moderate heat until tender, 25 minutes. Drain and spread out on a work surface or baking sheet. Let dry for 5 minutes.
Meanwhile, spread the almonds in a pie plate and toast in the oven for about 7 minutes, until golden. Let cool. Transfer the celery root to a food processor. Using a slotted spoon, add the cooked garlic, then add the toasted almonds and lemon juice and puree. With the machine on, gradually pour in the garlic-infused olive oil. Season the skordalia with salt, stir in 1/4 cup of water and serve.
The skordalia can be refrigerated overnight. Reheat gently.