Bring ½ cup water to boil in microwave. Add dried porcinis and submerge in the water. Allow mushrooms to sit and reconstitute for at least 30 minutes. Meanwhile, preheat oven to 400 degrees.
Unroll pie crust and roll to a 15" circle. Wrap the crust around a rolling pin and transfer to a baking sheet lined with parchment paper and set aside.
Use a slotted spoon to remove porcinis from liquid and chop coarsely, reserving the mushroom broth. Place a large skillet over medium-high heat and melt butter. Add porcini and criminis and cook for about 10 minutes, stirring occasionally until mushrooms are tender and dark brown in color.
Add diced red onion, garlic, thyme and pepper and cook an additional 2 minutes. Add sherry or wine, Worcestershire and reserved porcini broth, making sure not to add any sediment that has collected on the bottom. Boil for 2–3 minutes until liquid is evaporated. Remove from heat and set aside to cool.
Sprinkle half of the shredded Asiago into bottom of the rolled out pie crust then top with cooked mushrooms. Spread the filling out so it stops 2" from the edge of the dough. Fold the remaining dough up and over the mushrooms, folding and pleating as you work around the tart. Beat one egg thoroughly and brush egg wash over the exposed crust, going under the folds to help them stick together.
In a small bowl, whisk cream and remaining 2 eggs until smooth then pour into crust. Top with remaining Asiago and bake about 30 minutes until set and the top is golden. Cool at least 15 minutes prior to serving.
One Last Thing
Dried porcinis are affordable and give the mushrooms a very rich flavor!