Spring Onion Gratin Recipe

Onions baked in cream and topped with crunchy breadcrumbs is a classic, luxurious side. My version bathes tender scallions in aromatics like garlic, thyme and tarragon and accentuates the silky result in Parmesan laced croutons. -- Vivian Howard

This recipe is featured in the Onions and Avetts episode of Season 4 of A Chef's Life.

Ingredients

2 cups heavy cream
2 cups whole milk
5 garlic cloves, smashed
3 sprigs thyme
4 sprigs tarragon, divided
6 black peppercorns
2 teaspoons salt, divided
12 scallions
6-8 turns of the black pepper mill
1 loaf sourdough or other rustic style bread
3 tablespoons unsalted butter, melted
Zest of 2 lemons, removed with a microplane
3 cup grated Parmigiano Reggiano

Directions

Preheat your oven to 375 degrees. In a 2-3- quart saucepan, combine the heavy cream, milk, garlic, thyme, half the tarragon, the black peppercorns and 1 teaspoon salt. Bring that up to just below a simmer and let it steep for 30 minutes. It will reduce and thicken slightly. Do your best to prevent it from boiling. If it does accidentally come to a boil, you’ll have a mess to clean up.
Trim the hairy root end away from the scallions, and cut them in half, separating the dark green ends from the white. Tuck the scallions into a 2-3- quart baking dish. Strain the heavy cream mixture, discarding the solids, and carefully pour it over top. The scallions should wading in the cream, their chests barely peeking out, rather than bobbing around in an ocean of it. Adjust by scooping out some liquid or adding a little straight cream from the carton if necessary. Pick the leaves from the remaining tarragon and sprinkle them evenly over top. Season the scallions with the black pepper and ½ teaspoon salt.
Cut the bread into ½ inch cubes. You’ll need roughly 4 cups of these. Toss them with the butter, the lemon zest, Parmigiano Reggiano and the remaining ½ teaspoon salt. Spread the bread evenly over top of the scallions and slide the whole thing onto the middle rack of your oven. Bake uncovered for 30-40 minutes. The bread should crisp up and brown and the scallions should be bubbling and fragrant in the cream. Serve warm.