On the day you wish to eat the salad, make the dressing. In a small glass bowl, whisk together the yolk and vinegar, then slowly whisk in the olive oil to emulsify.
Once all oil is incorporated, cover bowl and set aside in fridge.
Chicken salad with Vouvray, leeks and wheatberries
Meanwhile, slice the leeks in half lengthwise and then chop in 1/2 inch pieces, to make short and narrow leek ribbons. Rinse well in colander to remove grit.
In a medium skillet, heat oil and add leeks. Cook over medium heat, stirring occasionally, until leeks start to caramelize and turn golden.
While leeks are cooking, wash and dry the chicken breasts and lightly salt and pepper on both sides.
When the leeks are soft and golden, add the chicken breasts to the pan, then add the Vouvray to cover the pan bottom, plus a little extra. Cover the pan and turn the heat down to a low simmering boil. Poach the chicken in the wine until done, about 7 minutes or so, depending the the thickness.
When the chicken is done, remove from the pan, shred, and let cool on a plate. Add the leeks and poaching liquid to the cool wheatberries and fluff. (If you want a cold salad, now's the time to put the chicken and the wheatberries in the fridge to get cold. But I never wait that long and just eat it at room temp.)
When you wish to eat the salad, combine the cool/cold chicken with the cool/cold wheatberries and leeks and fluff with a fork. Mix in the cold white wine mayo dressing to taste. (I never need as much as I've made, but go for it if you love mayo.) Add salt and pepper to taste. Fold in the tiny grapes carefully, so as not to burst. Serve on a bed of mixed greens with a glass of chilled wine.