Lightly butter the tart tin and place parchment paper on the bottom.
Heat skillet over medium heat, add bacon and cook until tender but not crispy. Transfer to a plate and set aside to cool.
In the same skillet, add olive oil and sauté onions until translucent and tender but not caramelized. Next stir in mushrooms and cook until mushrooms are tender. Set aside to cool.
In a small bowl, whisk together eggs, heavy cream, dijon mustard, and chopped thyme. Stir in gruyere, ground pepper and mix until well combined.
Preheat oven to 400°. On a well-floured surface, roll out puff pastry large enough to fit the deep dish tart tin. Carefully transfer the pastry to the tin and gently press the bottom and sides with your fingers to line the tin. Use a fork to dock bottom of the pastry. Leave at least 1½" of extra pastry to hang over the tin. Gently press the pastry to the side of tart tin. Layer the quiche with bacon, onion mixture, kale and sprinkle sundried tomatoes on top. Sprinkle salt over the filling then pour the egg custard.
Bake the quiche on the middle tack for 20 minutes, then cover the quiche loosely with foil to prevent pastry edges from burning. Bake for additional 25-30 minutes or until the filling is set.
Let the tart cool for 20 minutes in the tin then serve.