Remove the butter from the refrigerator to soften. Preheat the oven to 450°F. Wash and dry the fresh produce. Halve the potatoes lengthwise. Pick the rosemary leaves off the stems; roughly chop the leaves. Using a zester or the small side of a box grater, finely grate the lemon to get 2 teaspoons of zest (or 4 teaspoons for 4 servings). Quarter and deseed the lemon(s). Roughly chop the onions.

Line a sheet pan with foil. Transfer the halved potatoes to the foil. Drizzle with olive oil; season with salt and pepper. Toss to coat; arrange in an even layer. Roast 20 to 24 minutes, or until browned and tender when pierced with a fork. Transfer to a bowl; add the softened butter, lemon zest,and chopped rosemary. Stir to coat. Taste, then season with salt and pepper if desired.

Meanwhile, pat the steaks dry with paper towels; season with salt and pepper on both sides. In a medium pan (or large for 4 servings), heat a drizzle of olive oil on medium-high until hot. Add the seasoned steaks. Cook 4 to 6 minutes per side for medium-rare (125°F), or until browned and cooked to your desired degree of doneness.* Leaving any browned bits (or fond) in the pan, transfer to a cutting board. Let rest at least 5 minutes.

*The USDA recommends a minimum safe cooking temperature of 145°F for steak. Cook the steaks an additional 2 to 3 minutes to achieve this. 
Consuming raw or undercooked meat, poultry, fish, seafood or eggs may increase your risk of foodborne illness. 

In the pan of reserved fond, heat a drizzle of olive oil on medium-high until hot. Add 1/4 teaspoon of black pepper (or 1/2 teaspoon for 4 servings). Cook, stirring frequently, 1 to 2 minutes, until fragrant. Carefully add the chopped onions, vinegar, broth concentrate, and 1/3 cup of water (or 2/3 cup for 4 servings). Cook, stirring frequently, 2 to 4 minutes, or until combined. Turn off the heat. Taste, then season with salt and pepper if desired.

Find the lines of muscle (or grain) on the rested steaks; slice crosswise against the grain. Serve the sliced steaks with the finished potatoes. Top the steaks with the pan sauce. Serve the lemon wedges on the side. Enjoy!