Place pie crust in 9-inch glass pie pan as directed on box for One-Crust Filled Pie. Brush mustard over bottom of crust. Brush edge of crust with milk. Press 1 tablespoon sesame seed onto crust edge.
Place oven rack in lowest rack position in oven; heat oven to 400°F. In 8-inch skillet, melt butter over medium heat. Add onions; cook and stir until crisp-tender. Stir in spinach, ham and thyme. Reduce heat to low; cook until spinach is thoroughly heated. Spread spinach mixture over mustard in bottom of crust.
In small bowl, beat flour, pepper, nutmeg, whipping cream and eggs with wire whisk until well blended. Pour egg mixture over spinach layer. Sprinkle with cheese and 2 tablespoons toasted sesame seed.
Place quiche on lowest oven rack in oven; bake 35 to 40 minutes or until knife inserted in center comes out clean and crust edge is deep golden brown. After 15 to 20 minutes of baking, cover crust edge with strips of foil to prevent excessive browning. Cool 5 minutes before serving.