Remove any brown spots from potatoes, then peel and cut potatoes into 1-inch pieces.
To a large pot, add potatoes, 2 tsp salt and enough water to cover (by approx. 1 inch) (use same for 4 servings). Cover and bring to a boil over high.
2
Meanwhile, to a large bowl, add half the vinegar, 1/4 tsp (1/2 tsp) sugar and 1/2 tbsp (1 tbsp) oil. Season with salt and pepper. Stir to combine.
Top with spinach and salad topping mix. Set aside in the fridge until step 6.
3
Once water is boiling, reduce heat to medium-high. Simmer uncovered for 10-12 min, until fork-tender.
Drain and return potatoes to the same pot, off heat.
Roughly mash 2 tbsp (4 tbsp) butter and 3 tbsp (6 tbsp) milk into potatoes until slightly mashed. (NOTE: 'Smashed' potatoes will still have a few chunks!)
Season with salt and pepper.
4
Meanwhile, pat steaks dry with paper towels, then season all over with salt and pepper.
Heat a large non-stick pan over medium-high.
When hot, add 1 tbsp (2 tbsp) oil, then steaks.
Pan-fry for 4-7 min per side, or until cooked to desired doneness.** (NOTE: If steaks brown too quickly, reduce heat to medium.)
When steaks are done, remove from heat and transfer to a plate. Loosely cover with foil and set aside to rest for 2-3 min.
5
Meanwhile, reheat the same pan over medium-high.
When hot, add 1 tbsp (2 tbsp) oil, then mushrooms.
Season with salt and pepper. Cook for 5-8 min, stirring often, until softened.
Add garlic puree, shallots, flour and 1 tbsp (2 tbsp) butter. Cook for 1-2 min, stirring often, until shallots soften slightly.
Reduce heat to medium, then stir in 2/3 cup (1 1/3 cups) water, broth concentrate, remaining vinegar and any beef resting juices.
Bring to a simmer. Cook for 3-4 min, stirring occasionally, until gravy thickens slightly.
6
Toss salad.
Thinly slice steaks.
Divide steaks, salad and smashed potatoes between plates.