Feeling a bit stuffed after the big holiday meal? Pass around a tangy and refreshing salad like this one; it will reset appetites and get everyone excited for dessert.
In a large bowl, whisk together buttermilk, crème fraîche, and lemon juice; generously season with salt and pepper. Slowly whisk in oil. Gently toss lettuce leaves and hearts and sliced fennel with dressing, then add half each of fennel fronds, parsley, and marjoram and toss again.
Arrange salad on a platter; sprinkle with lemon zest and remaining fennel fronds and herbs. Season to taste. Serve immediately.
The dressing can be made and refrigerated in an airtight container up to three days ahead; bring to room temperature before serving. For even and thin fennel slices, use a mandoline.