1. Prepare the ramekins/cups: If using ramekins (for molding panna cotta), lightly grease with cooking spray, wiping out most of the residue with a paper towel. Alternatively, arrange plastic cups on a tray.
2. Bloom the gelatin: Pour 1 cup of the half-and-half into the saucepan and sprinkle the powdered gelatin evenly over top. Let soften for 5 minutes or until the surface of the milk is wrinkled and the gelatin grains look wet and slightly dissolved. (If doubling the recipe, this may take longer)
3. Dissolve the gelatin: Set the saucepan over low heat and warm the milk gently, whisking frequently until the gelatin dissolves. Do NOT let the milk boil or simmer; if you see steam remove the pot from the stove immediately and let it cool down. The milk should get warm, but not so hot that you can't leave your finger in the pot for a few seconds. The gelatin will dissolve quickly as the milk warms. (The ideal temperature for me was just above the lowest setting. Pay close attention to the milk temperature on this step.)
4. Check to make sure the gelatin is dissolved: After about 2-3 minutes of warming, rub a bit of the milk between your fingers to make sure it's smooth; Or dip a spoon in the milk and check the back for distinct grains of gelatin.
5. Dissolve the sugar: Stir the sugar into the milk and continue warming until dissolved. Again, never let the mixture boil or steam.
6. Remove the saucepan from the heat. Whisk in the remaining half and half, vanilla, and a pinch of salt.
7. Pour into cups/ramekins and chill: Divide the mixture evenly between the prepared ramekins or cups and refrigerate. If serving straight from the cups, without unmolding, chill for 1 to 2 hours. If you want to unmold the panna cotta, chill for at least 4 hours or overnight.

Optional

1. Prepare to unmold: Fill a large bowl partway with warm to hot water. Wipe a dessert plate with a damp paper towel (a damp plate lets you reposition the panna cotta more easily if it doesn't fall in the right spot).
2. Release the panna cotta edge from the cup: Run a thin knife carefully around the sides of a ramekin. Don't slide the knife all the way into the cup; just release the top edge of the pudding from the edge of the cup. Dip the ramekin in the warm water up to its rim, and hold it there for about 3 seconds.
3. Unmold on a plate: Invert the ramekin over the plate and shake gently to help the panna cotta fall out, or press gently on one side to help nudge it out. It should fall out on the plate easily. (If it does not, return to the warm water bath in increments of 2 seconds.) Reposition on the plate if desired. Serve immediately, or refrigerate, lightly covered, for up to 5 days. The gelatin gets stronger as it sits, so this will be a bit rubbery by days 4 or 5, but you can mitigate this by letting the panna cotta sit at room temperature for about half an hour before serving.