Heat olive oil in a large skillet, once hot, add leeks and sauté until tender, add mushrooms and cook until they release their juices, add ½ tsp salt, add wine and cook until reduced and most of the wine has evaporated. Add herbs and stir to combine and set aside to allow to cool.
Place brioche on baking sheet and toast for 15 minutes. Set aside and allow to cool.
In a large bowl, whisk together eggs, add milk, cream and remaining ½ tsp of salt.
Add mushroom mixture to egg mixture. Stir to combine, add brioche, stir to combine.