Hi Elenor. Here's a suggestion.
I frequently make a version of duxelles to use for a variety of things, including tartlets. I clean and trim a pound or so of mushrooms and in a food processor chop them finely (about 1/8" pieces). Then chop an onion into pieces the same size. Put the mushrooms and onions in a saute pan with a few tablespoons or half stick of butter, a generous 1/4 teaspoon of thyme, and salt pepper to taste, and cook them until the liquid is almost completely evaporated. Then I freeze the mixture.
Later you can thaw the mushrooms and use them in pasta, sauces, tarts, etc. I have made tartlets in a a variety of crusts including won tons and even wrapped in puff pastry.
For making tartlets you can actually use them plain, but if you want to make them more cohesive, you can add a little egg mixed in milk or cream to make a custard. You could also add cheese to the mushrooms with or without the custard.
This is so easy to do, plus you can make the duxelles ahead of time - even watch for mushrooms on sale. And, of course, you can vary it to your taste - more or less thyme, or a different herb, or leave it out, etc.
I would suggest freezing the duxelles in individual batches to use as you need them.
Hope this helps.