Mix together 1 tablespoon of the beef tallow, 1/2 teaspoon of kosher salt, 1 teaspoon of the Herbes de Provence, and the potatoes in a baking dish. Allow the potatoes to roast for 25 minutes.
After 25 minutes, mix in the leeks with the potatoes and allow to bake for 5 minutes more.
While the potatoes are roasting heat a large skillet on high heat. Add 1 tablespoon of beef tallow and allow to heat through and melt.
Season both sides of the steaks with the remaining kosher salt and black pepper.
Allow the steaks to cook 3-4 minutes on the first side before flipping.
Cook them an additional 3-4 minutes on the second side, depending upon how well done you like your steaks.
Allow the steaks to rest for 10 minutes.
While the steaks are resting mix together the softened butter with the remaining Herbes de Provence. Top the resting steaks with the butter.