In a medium bowl, combine the ricotta, scallions, dill, chives, 1 teaspoon salt, and 1/2 teaspoon pepper and set aside for up to 30 minutes.
With a small serrated knife, cut the larger tomatoes in wedges through the stem and the smaller tomatoes in half through the stem. Place them in a medium bowl with the garlic, olive oil, 1 teaspoon salt, and 1/2 teaspoon pepper and set aside.
When ready to serve, add the basil to the tomatoes and combine. Pile the ricotta in a large (12-inch) round shallow bowl or oval platter. Using a slotted spoon, place the tomatoes around the ricotta, discarding any liquid. Drizzle the tomatoes and ricotta with olive oil, sprinkle with the reserved basil and fleur de sel, and serve at room temperature.
Set a fine-mesh sieve over a deep bowl. Dampen 2 pieces of cheesecloth with water and line the sieve with a double layer of the cheesecloth.
Pour the milk and cream into a medium stainless-steel or enameled pot, such as Le Creuset, and stir in the salt. Bring to a full rolling boil over medium heat, stirring occasionally. Turn off the heat and pour in the vinegar. Allow the mixture to stand for one minute, until it curdles. It will separate into thick parts (the curds) and milky parts (the whey).
Pour the mixture into the cheesecloth-lined sieve and allow it to drain into the bowl at room temperature for 20 minutes (for soft ricotta) to 25 minutes (for firmer ricotta), occasionally discarding the liquid that collects in the bowl. Transfer the ricotta to a bowl, discarding the cheesecloth and any remaining liquid. Use immediately or cover with plastic wrap and refrigerate. The ricotta will keep, refrigerated, for 4 to 5 days.