Begin by bringing a large pot of salted water to a rapid boil over high heat. Once boiling, add your preferred pasta shape and cook according to package instructions, typically around 8-10 minutes. Stir occasionally to ensure the pasta doesn’t stick. When al dente, drain the pasta, saving a cup of the starchy pasta water for later.

While the pasta cooks, heat a medium saucepan over medium heat and melt the butter. Once fully melted, whisk in the flour, stirring constantly until it bubbles lightly, about 1 minute. Gradually pour in the milk, continuing to whisk until the mixture thickens, approximately 2-3 minutes. Season with a pinch of salt.

Once the white sauce has reached a creamy consistency, remove from heat. Stir in the pesto until fully combined.

Return the drained pasta to the pot. Pour the creamy pesto sauce over the pasta and gently toss to coat. Add reserved pasta water if the mixture feels too thick.

Spoon into bowls and garnish as desired, such as with grated Parmesan cheese or fresh vegetables. Serve warm.