For the reduction: Combine 1 cup water, the wine, dill, mustard, vinegar, honey and sugar in a wide saucepan. Simmer over medium heat until the sauce has thickened and reduced down, 10 to 15 minutes. Keep warm.
Meanwhile, grill the steaks over high heat for about 4 minutes per side. Remove and let rest for 10 minutes.
For the potatoes: Mix the potatoes with the dill, oil and some salt and pepper. Grill in a grill basket until browned, 10 to 15 minutes.
Place the steaks on plates and pour the reduction over. Serve with the dill potatoes and garnish with parsley if using.