Unroll piecrust onto a lightly floured surface. Roll into a 12-inch circle. Place in a deep-dish 9-inch pie plate; fold edges under and crimp. Prick bottom and sides of piecrust with a fork. Bake for 6 to 8 minutes.
Reduce oven to 375°.
In a large skillet, melt butter and olive oil over medium-high heat. Sauté garlic, onion, and mushrooms until tender. With a slotted spoon, remove vegetables to a medium bowl, leaving as much oil in pan as possible.
Add diced chicken to pan, and cook until lightly browned; remove from pan, and set aside.
In a small bowl, whisk together eggs, half-and-half, dry mustard, salt, and pepper.
To assemble quiche, sprinkle 1 cup cheese over bottom of prepared crust. Layer chicken and vegetable mixture on top of cheese. Pour egg mixture over chicken and vegetables. Top with remaining ½ cup cheese. Bake for 30 minutes, or until the middle is set.
Let cool for 10 to 15 minutes before serving.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/how-to-host-an-elegant-spring-luncheon/