Spray eight 8-oz. ramekins with cooking spray. Set aside.
Pour half and half into a medium sauce pan. Sprinkle gelatin over milk and allow to sit for about 5 minutes to soften gelatin. Whisk together over medium-low heat until gelatin dissolves. Do not allow the mixture to boil.
Add cream and sugar to the gelatin mixture and cook over medium heat, whisking until the sugar is dissolved. The mixture will be scalding, but not boiling. Remove from heat.
Add chopped chocolate to warm cream mixture and whisk until chocolate is melted and the mixture is smooth. Stir in vanilla.
Transfer mixture to a bowl with a pouring spout or a glass measuring cup, and evenly distribute the chocolate mixture among the eight prepared ramekins. Place ramekins into a large rectangular dish in order to keep them flat and for easier moving into and out of the refrigerator.
Allow the panna cotta to set up for at least 4 hours, or overnight until firm. If you plan to refrigerate them overnight, be sure to cover each ramekin with plastic wrap to prevent a skin from forming on the panna cotta.
When ready to serve, place each ramekin into a bowl of hot water for about 1 minutes to loosen the pudding from the ramekin. Take care not to get any water into the panna cotta.
Remove the ramekin from the water and dry off the bottom with a paper towel. Then, invert the serving plate over the top of the ramekin and invert, shaking a little bit to loosen the panna cotta from the ramekin. You may also have to run a knife around the edges. Lift the ramekin off the panna cotta and you should have a beautiful round dessert waiting to be garnished.
Garnish each panna cotta with a dollop of whipped cream and a spoonful of chocolate shavings.