How to Make It
Pour 1 cup of the half-and-half into a medium bowl. Sprinkle the gelatin all over the surface and let stand until dissolved, about 5 minutes.
In a medium saucepan, combine the remaining 3 cups of half-and-half with the goat cheese and a large pinch of salt and whisk over moderate heat just until hot to the touch and the cheese has melted. Whisk the goat cheese cream into the gelatin cream until blended. Pour the panna cotta into eight 4-ounce ramekins and refrigerate until set, about 2 hours.
Meanwhile, in a large bowl, toss all of the tomatoes with the olive oil, shallot, chives and basil and season with salt and pepper. Let stand at room temperature for 1 hour, stirring occasionally.
Pour about 3 inches of boiling water into a shallow heatproof bowl. Dip the bottom of each ramekin into the water for 5 seconds, then invert the ramekins onto plates and shake gently to unmold the panna cottas. Spoon the tomato salad over and around each panna cotta, top with the baby arugula and serve.