I have successfully made this recipe by cooking the lemons in my Instant Pot pressure cooker (affiliate link) for 6 minutes on high pressure with natural release. While I haven't tried the microwave method, I've read comments made on the New York Times orange almond cake version of the recipe that suggest you can cook the lemons in a large bowl of water in the microwave for 10-15 minutes as well. Please let me know if you try the microwave method and I can update the information here accordingly. I do find it easy to boil the lemons in a pot of water on the stove for an hour. Once they reach a low boil, they let off a lovely scent that freshens the house with lemon. The important bit, no matter your method, is to make sure your Meyer lemons reach a very soft, slumped consistency (while still whole) with an almost jammy interior.