01 - Heat olive oil in a large saucepan or Dutch oven over medium heat. Add the finely chopped onion and sauté for 3-4 minutes until softened and translucent.
02 - Add the minced garlic to the saucepan and cook for an additional 1 minute until fragrant, being careful not to burn it.
03 - Stir in the orzo pasta and toast it in the pan for 1 minute, stirring constantly. Add the pumpkin purée, dried thyme, ground nutmeg, and a generous pinch of salt and black pepper. Stir to combine.
04 - Pour in the vegetable broth and milk. Stir everything together thoroughly. Bring the mixture to a gentle simmer, then reduce the heat to low. Cook uncovered, stirring frequently, for 12-15 minutes, or until the orzo is tender and has absorbed most of the liquid.
05 - Add the roughly chopped baby spinach to the saucepan. Continue to cook for 2-3 minutes, stirring until the spinach has wilted into the orzo mixture.
06 - Remove the saucepan from the heat. Stir in the freshly grated Parmesan cheese and unsalted butter until they are fully melted and the orzo is creamy. Taste and adjust the seasoning with additional salt and pepper if needed.
07 - Serve the one-pot orzo immediately. Garnish with extra grated Parmesan cheese, if desired.