No, it’s not a sauce named after your weird uncle or your childhood crush. Sauce Robert (imagine how the French might say it: Roh-bear) is a mustard sauce with shallots and white wine, a classic in French cuisine. It’s served over a seared sirloin and next to mashed blue cheese and chive cauliflower. Yum yum.
Remove leaves from cauliflower head, core, and cut into large florets. Add cauliflower florets to boiling water and cook until tender, 6-8 minutes. While cauliflower boils, mince chives. Peel and halve shallot. Slice halves into thin strips. Trim ends off green beans. Pat steaks dry, and season both sides with a pinch of salt and pepper.
Mash the Cauliflower
Drain cauliflower in a colander and return to pot. Add blue cheese, half the milk, half the butter (reserve remaining for sauce), and chives (reserving a pinch for garnish). Mash, adding remaining milk 1 Tbsp. at a time, until desired consistency is reached. Set aside.
Cook the Steaks
Heat 1 tsp. olive oil in a medium non-stick pan over medium-high heat. Add steaks to hot pan and cook until steaks reach a minimum internal temperature of 145 degrees, 3-4 minutes per side. Remove steaks to a plate and cover with foil. Reserve pan; no need to wipe clean.
Make the Sauce Robert
Return pan used to sear steaks to medium heat. Add remaining butter and melt. Once melted, add shallots and stir occasionally, 1-2 minutes. Add white wine and cook until mostly evaporated, 30-60 seconds. Add demi-glace and Dijon and stir until thick enough to coat the back of a spoon, 1-2 minute. Remove from burner and set aside.
Cook the Green Beans
Heat 1 tsp. olive oil and 2 Tbsp. water in another medium non-stick pan over medium heat. Add green beans to hot pan. Once beans start sizzling, cover and cook until tender, 5-7 minutes. Season with a pinch of salt and pepper.
Finish the Dish
Add mashed cauliflower and green beans to a plate. Nestle steak onto mashed cauliflower and drizzle with sauce Robert. Garnish cauliflower with remaining chives.