Create a reduction: Peel and finely dice the shallot. Lightly crush the peppercorns with the blade of a large knife or in a mortar. Bring 3 tablespoons of water, vinegar, diced shallots and peppercorns to the boil in a small pot. Boil down until the liquid is reduced to about 1/3. Pour reduction through a fine sieve into a metal bowl and let it cool down for about 10 minutes.
Clarify butter: To do this, melt the butter at low heat until it separates into three layers - an upper foam layer of egg white, a middle layer of yellow butterfat and the whey that settles at the bottom. Skim off the upper foam. Then slowly pour the concentrated butter into a measuring cup so that the whey remains in the pot.
Mix the egg yolk with the reduction. Whisk in a hot water bath (60-70°C) with a whisk until a thick, creamy foam is formed (approx. 3 minutes). The temperature should remain constant, as the sauce does not gain volume if the heat is too low. Too much heat will cause the sauce to curdle.
Beat clarified butter first drop by drop and then in a thin stream under the egg yolk mass. Season to taste with lemon juice, possibly Worcester sauce, salt and pepper. Keep the sauce warm on a bain-marie. If the hollandaise thickens too much, stir in some warm water in a thin stream.
Prepare sauce hollandaise and season to taste with mustard. Toast the slices of bread in portions. Grate cheese roughly.
Spread 4 slices of bread thinly with some hollandaise sauce. Spread the ham and half the cheese on the 4 coated slices. Place the remaining 4 slices of bread on top. Pour the rest of the hollandaise sauce on top and sprinkle with the rest of the cheese. Bake under the hot oven grill for about 10 minutes.
In the meantime, sort out the salad, wash and drain. Clean and wash the radishes and cut them into fine sticks. For the vinaigrette, peel and finely dice the shallot. Mix vinegar, salt, pepper and honey. Fold in the oil. Stir in the shallot.
Mix vinaigrette with salad and radishes. Halve the croques and serve with the salad.