Place the sun-dried tomatoes in a small bowl and cover with very hot water. Let sit to rehydrate while you prepare the orzo.
In a large Dutch oven or similar large, heavy-bottomed pot with a tight-fitting lid, heat the oil over medium-high heat. Once the oil is hot but not yet smoking add the onion and sauté until fragrant and beginning to soften, about 3 minutes. Add the orzo, garlic, salt, and black pepper. Sauté, stirring to combine the ingredients and coat the orzo with the onion and oil. Cook just until the garlic is fragrant, about 30 seconds. Be careful not to let the garlic burn.
Slowly stir in the milk and 2 cups of the broth. Bring to a gentle boil, stirring very frequently with a wooden spoon and scraping the spoon along the bottom of the pot to prevent the orzo from sticking. Cover the pot and reduce the heat to a light simmer. Cook until the orzo is al dente, most of the liquid is absorbed, and the orzo is very creamy, 8 to 10 minutes. Lift the lid every few minutes to stir and run the spoon along the bottom to prevent sticking If the pasta looks dry at any point, add several splashes of broth as needed to loosen it.
Drain and roughly chop the sun-dried tomatoes. Add them to the pot. Stir in the spinach, red pepper flakes, lemon zest and juice, Parmesan, and half of the basil. Continue to cook and stir until the spinach is just wilted and the cheese melts, about 1 minute. Taste and season with additional salt, black pepper, and red pepper flakes as desired. Serve hot, sprinkled with the remaining basil and additional Parmesan.
Store leftovers in a tightly covered container in the fridge for up to 3 days. Reheat gently on the stove top or in the microwave with a splash of water, broth, or milk if pasta seems a little dry.
Makes 8-10 side dish servings.
Recipe used with permission from The Well Plated Cookbook by Erin Clarke, published by Avery, an imprint of Penguin Random House LLC.