Seared Flat Iron Steak with Asparagus Gratin

Last Updated on November 12, 2023

It’s hard not to love the pairing of a beautifully seared, caramelized steak with a rich and creamy gratin.

This gratin features spring vegetables like young onions and asparagus in a cream sauce richly seasoned with garlic, thyme and anchovy. (Don’t be scared off by the anchovy–it’s a small amount that adds just the right hit of umami.)

Make this dish for a special date night, or whenever you feel like an indulgent dinner. Swap snap peas for the asparagus, if you like. The lemon wedges are optional, but a squeeze of their fresh juice offers a bright contrast to all the richness in the dish.

Seared Flat Iron Steak with Asparagus Gratin

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Protein: Beef
Cut: Flat Iron
Course: Main Course
Prep Time: 20 minutes
Cook Time: 40 minutes


  • 2 6-ounce ButcherBox flat iron steaks defrosted, patted dry
  • salt and pepper
  • 3/4 cup coarse raw breadcrumbs
  • 1 tbsp olive oil
  • 1/2 bunch medium-thick asparagus trimmed
  • 1 tbsp unsalted butter
  • 2 tbsp canola oil or another high heat oil
  • 1/2 cup spring onion cut into thin rings
  • 2 cloves garlic finely chopped
  • 2 oil-packed anchovies drained, finely chopped
  • 1 cup heavy cream
  • 1 tsp fresh thyme leaves
  • lemon wedges for serving, optional
  • Flaky sea salt optional


  • Preheat the oven to 350ºF. Season the steaks generously with salt and pepper. Cut the asparagus into 2-inch slices on a diagonal. Line a baking sheet with parchment.
  • Toss the bread crumbs with the olive oil on the baking sheet. Season with salt; toss again. Bake, tossing occasionally, until golden brown and toasted, about 10 minutes. Set aside to cool. Raise the oven temperature to 425ºF.
  • Melt the butter in a medium, oven-safe skillet over medium-low heat. Once melted, stir in the garlic and anchovy. Cook, stirring, until fragrant, about 2 minutes. Stir in the heavy cream and thyme; bring to a simmer. Add the asparagus and spring onions, season with salt and pepper, and gently toss with tongs to combine. Transfer the skillet to the oven and bake until the cream is bubbly, thickened and reduced slightly, and the top layer of the asparagus and spring onions are golden brown, 7 to 9 minutes. Set aside and let cool slightly. 
  • Meanwhile, heat a medium to large cast-iron skillet over high heat. Add the canola oil, swirl to coat the skillet, then gently lay the steaks down and sear, undisturbed, until the underside is deeply browned and caramelized and a crust has formed, about 4 minutes. Turn the steaks over and cook until the bottom side is about as browned and an instant-read thermometer stuck into the thickest parts reads 120ºF for medium-rare, about 2 minutes longer. Transfer the steaks to a cutting board, tent with foil and let rest for 10 minutes. 
  • When ready to serve, top the gratin with the breadcrumbs and divide among the serving plates, along with the lemon wedges, if using. Slice the steak against the grain and transfer to the plates. Season the steak with flaky salt and more black pepper, if desired.
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