Bistro Steak with Buttermilk Onion Rings

For vinaigrette, steak, and sauce:

Step 1

Whisk hazelnut oil and 1 tablespoon vinegar in a small bowl; season with salt and pepper. Set vinaigrette aside.

Step 2

Heat vegetable oil in a large skillet over medium-high heat. Season steak with salt and pepper and cook 6–8 minutes per side for medium-rare. Let rest 10 minutes.

Step 3

While steak rests, cook butter and shallot in same skillet over medium heat, stirring occasionally, until shallot is softened and starting to brown, about 4 minutes. Add thyme and peppercorns. Cook, stirring occasionally, until mixture is fragrant, about 2 minutes. Add remaining 1 tablespoon vinegar and 1/2 cup water and simmer until flavors meld and sauce is thick enough to coat a spoon, about 2 minutes. Remove sauce from heat and whisk in mustard; season with salt and pepper.

For onion rings and assembly:

Step 4

Fit a medium saucepan with thermometer; pour in oil to measure 3". Heat over medium-high heat until thermometer registers 350°F.

Step 5

Meanwhile, mix buttermilk and vinegar in a shallow bowl. Place flour in another bowl or baking dish; season with salt and pepper. Toss onion rings in flour mixture, shaking off excess, and transfer to a wire rack. Working in batches, dip in buttermilk mixture, letting excess drip back into bowl; toss again in flour.

Step 6

Working in 2 or 3 batches and maintaining temperature of oil, fry onion rings until golden brown and crisp, about 3 minutes per batch. Let drain on paper towels; season with salt.

Step 7

Toss watercress with reserved vinaigrette. Thinly slice steak against the grain. Serve steak with sauce, watercress, and onion rings.