In the superior part of a bain-marie, beside heat, whisk egg yolks and orange juice. Set over simmering water but not boiling.
Whisk until the preparation is hot and foamy. Add butter, one cube at a time. Whisk each time you add a cube until butter is melted. Season. Set sauce over warm water while cooking poached eggs.
In a large casserole, simmer water with vinegar. Break eggs into cups. Slide 2 eggs at a time into the water and poach for 3 to 4 minutes, until desired cooking. The yolks should normally be liquid. Lay the poached eggs over paper towels. Repeat the same thing with the remaining eggs.
Meanwhile, in a large pan, heat olive oil at high heat, brown leeks for one minute. Add white wine and reduce until almost dry. Set aside.
Slice english muffins in two and set aside.
Lay leeks mixture over demi english muffins, a ham slice or smoked salmon, then an egg. Keep warm in the oven for a few minutes, if needed.
When serving, coat with Hollandaise sauce.