Step 1

Preheat oven to 350°. Mix oil, butter, thyme, and garlic in a small bowl. Scatter bread on a large rimmed baking sheet and drizzle oil mixture over. Toss, squeezing oil mixture into bread; season with salt and pepper.

Step 2

Bake, tossing occasionally, until croutons are golden brown and crisp, 20–22 minutes. Let cool.

Step 3

Do Ahead: Croutons can be made up to 1 day ahead. Store airtight at room temperature.

Step 4

Shake oil, vinegar, mustard, and garlic in a jar to combine. Add 2 tsp. tarragon; season dressing with salt and pepper.

Step 5

Toss radicchio, fennel, beets, turnips, and lettuce in a large bowl to combine. Drizzle dressing over and toss to coat; season with salt and pepper.

Step 6

Toss in croutons and pomegranate seeds and serve topped with more tarragon.

Step 7

Do Ahead: Dressing can be made 3 days ahead; cover and chill. Vegetables can be sliced 1 day ahead; cover and chill.