Cabernet Sauvignon with steak: an unquestioned classic for a reason. The beefy, full-flavored bavette wants a substantial red wine with tannin, and the Cabernet butter helps complete the liaison.
Place wine, minced shallot, and a large pinch of pepper in a small saucepan on medium heat. Reduce wine mixture by three quarters. Add a pinch of salt and continue reducing until a few tablespoons of syrupy mixture remain. Set aside to cool.
Work the wine mixture into the softened butter. Add a squeeze of lemon and the chopped parsley. Chill to firm. May be made a few days in advance.
Remove the bavette steak and the butter from the refrigerator 45 minutes before cooking. Sprinkle the meat liberally with sea salt.
Heat a grill or grill pan to high. Lightly drizzle the steak with olive oil and grill until golden brown on both sides and cooked to medium-rare doneness. Let the steak rest for 10 minutes.
Slice the steak against the grain and lay the slices on a platter. Spoon the softened butter over the steak; the heat from the meat will slowly melt the butter. Place a small mound of fava leaves on top of the steak.
Accompany with roasted potato wedges with fennel.