Best Brunch Quiche

3 Tbsp shallot or onion, chopped 
2 cups flour 
2 tsp kosher salt, divided use 
½ lb butter, cold, unsalted, cubed 
¼ cup ice water 
½ lb bacon, chopped 
2 lbs assorted mushrooms, thinly sliced 
¼ tsp freshly ground black pepper 
¼ tsp ground nutmeg 
4 green onions, chopped 
1 tsp dried thyme 
8 oz Gruyère cheese, shredded 
4 cups half and half 
6 eggs, beaten 

Pulse flour and 1 tsp salt in a food processor. Add butter and mix to combine. Add water in two batches, until just incorporated. Flatten the pastry into an 8-inch disk, wrap in plastic and refrigerate until chilled, at least 1 hour.  

Heat oven to 375°F. Spray interior of a 9-inch springform pan with cooking spray. Transfer pastry to springform pan and press it firmly up the sides, trimming as necessary. Chill 15 minutes. Line pastry with parchment paper and fill with dried beans or rice. Bake the crust until lightly browned, about 40 minutes. Remove parchment and beans and bake additional 10 to 15 minutes until browned. Let cool.  

Reduce oven temperature to 325°F. Cook bacon in a large skillet over medium high heat until crisp; transfer to paper towel. Cook mushrooms in bacon fat about 5 minutes, stirring occasionally. Reduce heat to medium; add onions and thyme and cook, stirring often, until the mushrooms are tender, about 10 minutes. Season with salt and pepper; cool. 

Sprinkle ¼ cup of Gruyère on pastry shell. Whisk together half and half and eggs; season with 1 tsp salt, ¼ tsp pepper and nutmeg. Stir in bacon, remaining cheese and mushroom mixture into eggs. Pour into pastry shell. Bake quiche for about 1½ hours, or until brown on top and just set in the center. Let cool slightly in the pan. Cut quiche into wedges and serve warm or at room temperature.