In a medium skillet sprayed with cooking spray or olive oil spray, add the mushrooms and cook over medium heat stirring occasionally around 5 minutes. While the mushrooms are cooking slice and clean your leaks. I fill a clean bowl with cold water and add the sliced leeks into the water, moving around to get any of the dirt off. Drain in a strainer and rinse with cold water. Let excess water drip off. Add the leeks to the skillet with the mushrooms and cook an additional 4 to 5 minutes until the leeks are broken down some and tender. Add a little salt and pepper to taste. Remove from heat in a bowl and set aside.
Place a piece of parchment paper on your work surface and remove the puff pastry from the fridge. Gently roll out to stretch out slightly to even out and make a bit larger of rectangle. Don't work too much or make too thin. Using a pizza cutter or knife, cut around 4 to 4.5 inch squares in the dough. You will get 9 squares in each sheet. Place the puff squares in the prepared muffin pan pressing down the bottom and up the sides.
Fill the Cups:
Using a ladle or ¼ cup measuring cup fill the tin with the custard. Fill ¾ of the way full. Bake for 30 to 35 minutes rotating halfway through if two tins, top to bottom, front to back. Remove from oven when the custard is completely set and the puff pastry is golden brown.
Let sit at room temp for about 5 minutes, carefully remove from tins using off-set spatula or knife and place on your serving dish. Serve warm.
Enjoy!
Recipe by Social Buttercream at https://socialbuttercream.com/2020/04/25/puff-pastry-egg-cups-put-an-egg-in-it/