For the ricotta cheese, stack 4 large squares of cheesecloth in a colander, leaving overhang.
Combine milk and buttermilk in a heavy large pot. Place pot over high heat. Stir almost constantly as mixture heats and curd begins to form.
When temperature registers 175-180 degrees F curds will separate from the whey and float to the top. Turn off heat.
Using a slotted spoon, transfer the curds to the prepared colander. Gather cheesecloth and press gently. Do not remove too much liquid or the ricotta will be dry. Let rest in colander 15 minutes.
Transfer ricotta to a storage container. Sprinkle with a little salt and stir. Cover and chill about 2 hours. Can be made a day ahead, keep chilled.
Combine the Basil Pesto and ricotta cheese.
Place tomato slices on a rimmed baking sheet, do not over crowd. Drizzle olive oil over tomatoes and season with salt and pepper. Cook under the broiler until slightly charred. Turn slices over and continue to broil until slightly charred on other side.
Toast pine nuts in a 400 degree oven for 4-6 minutes or until fragrant and golden brown.
Spread ricotta and pesto mixture over toast. Top with roasted tomatoes, pine nuts, freshly grated Parmesan cheese and basil leaves.