Roasted Root Vegetable Couscous with Horseradish Dressing

• 1 celeriac root bulb, peeled and sliced thin
• 1 golden beet bulb, peeled and sliced thin
• 1 bunch radishes (about 6–8), sliced thin
• 1 cup rainbow carrots, sliced (If you can’t find mixed rainbow carrots at the grocery store, orange carrots are fine.)
• ½ cup red onion, sliced
• 1 tablespoon olive oil
• 1 teaspoon kosher salt
• 1 teaspoon fresh ground pepper
• 2 cups pearled couscous, cooked and drained according to package directions
• 2 cups arugula, packed

Dressing:

• 2 tablespoons horseradish root, grated
• 3 tablespoons crème fraiche
• 1/3 cup olive oil
• 1 teaspoon honey
• 2 tablespoons lemon juice
• Salt and pepper, to taste