In a large pot of boiling salted water, cook pasta according to package instructions; drain well.
Heat olive oil in a large cast iron skillet over medium heat. Add garlic and onion, and cook, stirring frequently, until onions have become translucent, about 2-3 minutes.
Whisk in flour until lightly browned, about 1 minute.
Gradually whisk in milk, and cook, whisking constantly, until slightly thickened, about 3-4 minutes.
Stir in spinach until wilted, about 3 minutes.
Stir in Parmesan until melted, about 1 minute.
Stir in orzo; season with salt and pepper, to taste.
Serve immediately.
Notes
Cook the orzo until al dente. The orzo is cooked when it is tender but still firm with a chewy bite.
Add more vegetables and greens. Mushrooms, peas, zucchini, asparagus, broccoli and leafy greens (spinach, kale, collard greens, swiss chard or arugula) are all great additions.
Use high quality Parmesan. While powdered Parmesan can be a convenient option, it contains additives and fillers resulting in a gritty, sawdust texture. Opt for good quality, freshly grated Parmigiano Reggiano or domestic Parmesan – this gives that favorited rich, nutty flavor to the dish.
Stir often. Orzo releases quite a bit of starch during cooking. Frequent stirring will prevent the orzo from sticking and clumping, yielding even, creamy goodness.
Add a splash of liquid when reheating. Add a splash of water or milk (about 1 tbs per 1 cup orzo) to prevent from drying out.