Thaw pie crust for 15 minutes or follow directions on package
Preheat oven to 375°F. Place pie crust in a 9-inch pie dish or tart pan. Prick the bottom with a fork.
Par-bake the crust: Line with parchment and fill with pie weights (or dried beans). I use a special silicone mat. Bake 10 minutes.
Remove weights. Brush Dijon mustard on the bottom of the crust and bake 5 more minutes until lightly golden. Let cool slightly.
Sauté the shallots: In a small pan, melt butter and sauté shallots until soft, about 3 minutes. Let cool.
Make the custard: In a large bowl, whisk together eggs, cream, milk, salt, pepper, until smooth.
Assemble: Spread half the cheese on the bottom of the crust. Add ham and sautéed shallots. Pour custard over everything. Top with remaining cheese.
Bake: 35-40 minutes, until the center is just set (it will jiggle slightly but not be liquid). A knife inserted in the center should come out clean.
Cool: Let quiche rest 10-15 minutes before slicing. This allows the custard to set properly.
Serve: Slice into wedges and serve warm or at room temperature.