Fun party trick: Ask your friends to guess how many pounds of greens went into this fabulously cheesy gratin. Three humongous bunches of kale get drowned in garlic- and rosemary-infused cream, then blanketed in cheddar cheese and panko and placed into a hot oven, where they sizzle and shrink down.
- 1 medium onion
- 5 garlic cloves, divided
- 2 cups heavy cream
- 1 rosemary sprig
- 1½ tsp. kosher salt, plus more
- ½ tsp. freshly ground black pepper, plus more
- 4 medium or 3 large bunches of kale and/or Swiss chard (2–2½ lb. total)
- 1 lemon
- ¼ tsp. crushed red pepper flakes
- 6 oz. high-quality sharp cheddar cheese
- ½ cup panko (Japanese breadcrumbs)
- 1 tsp. extra-virgin olive oil
Preheat oven to 350°. First, prep the cream sauce: Peel and quarter 1 medium onion. Smash 4 garlic cloves and unpeel. Place onion and garlic in a medium saucepan. Pour in 2 cups heavy cream and stir in 1 rosemary sprig, 1½ tsp. Diamond Crystal or ¾ tsp. kosher salt, and ½ tsp. freshly ground black pepper. Simmer over low heat and cook, stirring occasionally, until onion and garlic are very soft, 15–20 minutes.
While cream cooks, remove ribs from 4 medium bunches of Tuscan kale. Tear leaves into big pieces and wash. It’s okay if some water still clings to the leaves—this will help them wilt later. If you don’t have a bowl big enough to hold all of your greens, pile them on a baking sheet instead.
When cream is ready, pluck out rosemary sprig and discard. Finely grate zest of ½ lemon into cream and stir in ¼ tsp. crushed red pepper flakes. Transfer to a blender and blend until smooth.
Heat a large (as large as possible—12″ is the goal) ovenproof skillet over medium. Add about one-quarter of greens, cover skillet (use a baking sheet if you don’t have a lid), and cook until wilted, 3–4 minutes. Scoot wilted greens to one side of pan. Add another quarter of greens, cover pan, and cook to wilt, 3–4 minutes. Remove from heat and place skillet on a rimmed baking sheet.
Pile remaining greens on top of wilted kale, press down to compact as needed. This will look CRAZY, but the greens shrink dramatically in the oven. Carefully pour cream mixture over. It’s okay if it drips a little—that’s why it’s on a baking sheet. Break cheese slices into large crumbles distributing evenly over top. Sprinkle panko mixture over.
Bake gratin until cheese is browned and bubbling and panko is toasted, 50–55 minutes.
Let cool 5 minutes before serving.