Prepare the ingredients. Drain and rinse the butter beans in a fine-mesh strainer. Mince the garlic, chop the sun-dried tomatoes, grate the Parmesan, and roughly chop the fresh basil. Having everything ready makes the cooking process easier.
Sauté the garlic and tomatoes. Heat the olive oil in a large skillet over medium heat. Add the minced garlic and cook for about 30 seconds until fragrant. Stir in the chopped sun-dried tomatoes, Italian seasoning, and red pepper flakes, if using. Cook for another minute, stirring frequently.
Add the butter beans. Stir the drained butter beans into the skillet, coating them with the garlic and tomato mixture. Pour in the vegetable broth and bring everything to a gentle simmer. Cook for 2–3 minutes to let the beans absorb some of the flavor.
Make the creamy sauce. Pour in the heavy cream and stir gently. Let the mixture simmer for 3–4 minutes until the sauce begins to thicken slightly. Keep the heat moderate and avoid a rapid boil.
Stir in the Parmesan. Add the freshly grated Parmesan cheese and stir until it melts into the sauce. Season with salt and black pepper, tasting before adding more salt because Parmesan already contains some.
Add the spinach. Stir in the fresh baby spinach and cook for 1–2 minutes until the leaves wilt into the creamy sauce. Fold gently to keep the butter beans intact.
Finish and serve. Remove the skillet from the heat and stir in the fresh lemon juice and chopped basil. Taste and adjust the seasoning if needed. Serve warm with crusty bread, toasted baguette slices, or your favorite side dish.