Thinly slice the apples. Toss with the lemon juice in a large bowl.
Make the dressing: Heat the olive oil in a skillet over medium heat. Add the shallots and 1/2 teaspoon salt and cook, stirring occasionally, until golden, about 8 minutes. Whisk in the vinegar and mustard; remove from the heat and let cool slightly. Whisk in the sour cream and 1/4 cup water.
Add the dressing to the bowl with the apples. Add the ham, watercress and endives. Season with salt and pepper and toss to coat.
Photograph by Con Poulos
Recipe courtesy Food Network Magazine