I think pastry crust would be a bit heavy for these, so I tend to use plain bread. These are easiest to eat if they're baked in bite sized mini cupcake tins, with a toasted bread crust holding all the onions in.
To make these, you will need:
16 slices of bread
3 large onions (I use yellow, whether regular or sweet)
2-3 T butter
a splash of apple cider (maybe 1/4 cup, more if you want more apple flavor to brighten the onion)
1/2 C or more of beef stock, preferably low sodium
4-8 oz shredded white cheese, depending on how much you like to add - I suggest mozzarella, provolone, swiss, havarti, or a combination of any of those
a few grinds of black pepper
bay leaf (optional)
Step 1: Make Crust
Depending on your preference, you can either roll the circles flat with a rolling pin or squish them flat as you press them into the muffin tins. Either way, lightly butter the bottom side to keep them from sticking, and to add a nice golden brown color to the crust.
Step 2: Cook the Onions
Melt a couple tablespoons of butter in a pan over medium heat and add onions. Stir every so often to make sure they don't burn. This part will take awhile. It would help to sprinkle a teaspoon of salt over the onions, but be careful. If your beef stock is salty, this might make the onions too salty. Let the onions gently cook down and turn a golden color. Add the thyme and bay leaf, if using. Grind on some black pepper.
After the onions are an even golden hue, add the apple cider and beef stock. Continue to cook the onions, letting the liquid evaporate. Once the onions are soft and the liquid has turned into a sticky glaze, taste them. Add salt if needed.
Step 3: Fill and Bake
Use a spoon to scoop the onion mixture into the crusts. Press the onion gently down to get rid of air pockets. These work best if the onion mixture is kept dense.
Sprinkle cheese over the onion pies. Make sure to clean up any onion or cheese that lands on the pan. It's a pain to scrub off after it's been baked on.
Bake for a few minutes until the cheese is melted and starting to turn golden. You can serve these warm or at room temperature.
Thanks for reading!