Drain the reconstituted dried mushrooms and chop into smaller pieces. Melt the butter in a frying pan and cook all the mushrooms and leeks over medium heat. When the mushrooms start to brown, add a little salt. This will all take around 5-7 minutes.
Toss in the Boursin cheese until melted. Set aside to cool slightly.
Meanwhile, whisk together the eggs and heavy cream. Add a little more salt and pepper (and any other seasoning you like). Add the veggies and stir until combined.
After the quiche crust (I use my 2.2.1 Keto Crust) has been blind-baked, pour in the filling, top with the grated parmesan, and bake for 30 minutes at 375 (or until brown).
Serve warm or at room temperature.