Wash and dry all produce. Adjust rack to middle position and preheat oven to 425 degrees. Line a baking sheet with aluminum foil. Quarter potatoes, then place on lined sheet. Toss with a large drizzle of olive oil, 1/2 tsp herbs de Provence (we’ll use the rest later), salt, and pepper. Roast in oven until crisp, 20-25 minutes.

Meanwhile, roughly chop garlic. Heat 1 TBSP olive oil in a medium pot over medium-high heat. Add garlic and cook, stirring, until fragrant, about 30 seconds.

Add spinach to pot and cook until just wilted, 1-2 minutes. Add flour and milk and stir well. Season with salt and pepper. Bring to a simmer and let bubble, stirring occasionally, until thick, about 2 minutes. Stir in both cheeses. Continue simmering until creamy and thick, about 2 minutes. Season with salt and pepper. Keep covered off heat.

Heat a large drizzle of olive oil in a medium pan over medium-high heat. Pat steak dry with a paper towel. Season all over with salt, pepper, and remaining herbs de Provence. Cook in pan until nicely browned on bottom, 6-7 minutes, then flip and cook on other side to desired doneness, 5-6 minutes more. Transfer to a cutting board and let rest.

While steak cooks, peel, halve, and thinly slice shallot. Pick parsley leaves and roughly chop; discard stems. Once steak is done, add a drizzle of olive oil to same pan over medium-high heat. Add shallot and cook until just softened, 1-2 minutes. Reduce heat to medium-low and stir in demi-glace, 1 TBSP balsamic glaze (we sent more), and 2 TBSP water. Season with salt and pepper.

Bring sauce to a simmer, then reduce heat to low. Add half the parsley and 1 TBSP butter, stirring to melt. Add up to 1 TBSP more water if sauce is stiff. Slice steak. Divide between plates along with potatoes and spinach (you may want to reheat it). Drizzle with sauce and garnish with remaining parsley.