1. Preheat oven to 400 degrees Fahrenheit.
2. Place the cherry tomatoes into a small roasting pan and toss with the tablespoon oil. Roast for 10 to 12 minutes, or until the tomatoes soften. Remove from the oven and toss with a little kosher salt. Set aside.
3. Place the garlic and pine nuts into the bowl of the food processor and process until finely ground. Scrape down the sides of the bowl. Add the basil leaves and process until the basil is in very tiny pieces. Scrape down the sides of the bowl again. Add the Parmesan cheese, salt and pepper, and process again for a few seconds. While the machine is on, slowly pour in the olive oil and process until it is all mixed in.
4. Cook the pasta al dente, according to package directions, and drain. Place into a large serving bowl.
5. While the pasta is cooking, heat the butter in a small or medium heavy saucepan over low heat. When the butter is melted, add the flour and whisk. Raise the heat to medium-low. Cook, whisking often, for three minutes. Reduce the heat if the mixture starts to color. Heat the milk in the microwave for about one minute, or until hot.
6. Add 1/4 cup milk to the saucepan and whisk in. Continue adding the milk, a little at a time, and whisk in. When all of the milk has been added, cook for about four minutes, or until thick, stirring often. If the mixture bubbles too much, reduce the heat. Add salt and pepper.
7. Whisk the pesto to the sauce, reserving two tablespoons to add later.
8. Add the sauce to the pasta and mix well.. Add more salt and pepper to taste. Mix in the roasted cherry tomatoes and reserved pesto. Sprinkle the sliced basil on top and mix in gently. Add Parmesan cheese on top.