Wash and dry all produce. Preheat oven to 425 degrees. Halve potatoes. Toss potatoes with a large drizzle of oil on a baking sheet. Season with salt and pepper. Arrange potatoes on baking sheet cut-side down. Roast in oven until crispy and browned, about 25 minutes.

Halve, peel, and mince shallot. Cut green beans into bite-sized pieces. Pick tarragon leaves from stems; discard stems. Finely chop leaves until you have 2 tsp chopped tarragon. Halve tomatoes lengthwise.

Heat 1 TBSP butter and a drizzle of oil in a large pan over medium-high heat. Add 2 TBSP shallot. Cook, tossing, until shallot is translucent, 2-3 minutes. Pour in 1 TBSP vinegar (we sent more) and allow to evaporate, 1-2 minutes. Stir in half the tarragon and cook until fragrant, about 1 minute. Remove from heat. Stir in mustard and sour cream.

Transfer sauce to a small bowl. Season with salt and pepper. Wipe out pan, then heat another drizzle of oil in it over medium-high heat. Pat steak dry with a paper towel. Season all over with salt and pepper. Add to pan and cook to desired doneness, 4-6 minutes per side. Remove steak from pan and set aside to rest. Wipe out pan

Add 1 TBSP butter and remaining shallot to same pan over mediumhigh heat. Allow butter to melt, then toss in green beans. Cook, tossing occasionally, until just barely tender, 3-5 minutes. Season with salt and pepper. Add tomatoes to pan and cook until softened, 2-3 minutes. Season with salt and pepper

Slice steak against the grain. Divide potatoes, veggies, and steak between plates. Spoon sauce over steak. (TIP: Give the sauce a stir first if it has separated.) Sprinkle with remaining tarragon (to taste) and serve.