Winter Greens Gratin

Ingredients

• 10 servings pepper black freshly ground
• 3 cups coarse salt fresh
• 2 teaspoons thyme sprigs fresh divided
• 7  garlic clove smashed
• 1 cup gruyere cheese grated
• 1 cup cup heavy whipping cream 
• 10 servings kosher salt 
• 2.5 pounds mustard greens 
• 0.1 teaspoon nutmeg freshly ground
• 0.3 cup olive oil extra virgin extra-virgin
• 0.5 cup parmesan finely grated
• 2  shallots sliced into 1/4"-thick rounds ( 1 cup)
• 24 cups kale trimmed chopped
• 1 tablespoon butter unsalted plus more for dish
• 1 cup milk whole

Equipment

• bowl
• frying pan
• sauce pan
• oven
• pot
• baking pan
• aluminum foil
• slotted spoon

Directions

1. Lightly butter a 3-quart baking dish. Workingin batches, blanch kale in a pot of boilinglightly salted water until just softened, about3 minutes. Using a slotted spoon, transferkale to a large bowl of ice water; let cool,then drain. Squeeze out as much excesswater as possible by hand and transfer kaleto a work surface.
2. Repeat with mustard greens, blanchingfor 2 minutes per batch. Coarsely chop allgreens and combine in a large bowl (youshould have 6 cups tightly packed greens).Separate clumps and loosen choppedleaves by hand.
3. Heat oil in a 12" skillet over mediumheat.
4. Add breadcrumbs and cook,stirring frequently, until golden and crispy,8-10 minutes.
5. Transfer to a large bowl;stir in Parmesan and 1 teaspoon thyme leaves.DO AHEAD: Greens and breadcrumbs canbe made 2 days ahead. Cover greens andchill. Store breadcrumbs airtight at roomtemperature.
6. Melt 1 tablespoon butter in a medium saucepanover medium-high heat.
7. Add shallots; cook,stirring often, until slightly softened and lightgolden, about 5 minutes.
8. Transfer shallotsto bowl with greens.
9. Add cream, milk, garlic,and thyme sprigs to same saucepan; bringto a simmer. Cook until mixture is thickenedand reduced to 1 1/2 cups, 10-12 minutes.Discard thyme sprigs and garlic; stir in nutmeg.Season mixture with salt and pepper.
10. Pour cream mixture over greens in bowland toss to evenly coat in sauce; season totaste with salt and pepper.
11. Transfer greensmixture to prepared baking dish; sprinkle
12. Gruyère over. Top with breadcrumbs. Coverdish with foil. DO AHEAD: Gratin can beassembled 1 day ahead.
13. Preheat oven to 400°F.
14. Bake until fillingis hot, about 25 minutes. Uncover and bakeuntil cheese is melted, edges are bubbling,and breadcrumbs are golden brown, 10-20minutes longer.
15. Garnish with remaining1 teaspoon thyme leaves.