Panna cotta is like a creamy vanilla pudding, but with none of the eggy flavor of a typical pudding, and also with a different texture: more cool and slidey because of the gelatin, more quivery and delicate. It is the perfect foil for summer fruits of all kinds, but especially raspberries, because then you don't have to do a single thing to them but toss them on top of the panna cotta.
In a very small saucepan sprinkle the gelatin over the water and let it stand about 1 minute to soften. Heat the gelatin mixture over low heat until the gelatin melts and dissolves and remove pan from heat.
In a medium-sized pot, bring the half and half and sugar just to a boil over moderately high heat, stirring. Remove the pot from the heat and stir in the vanilla and the gelatin mixture (I swirl a little of the hot cream mixture into the gelatin pot to get out the dregs). Divide the cream mixture among eight 1/2-cup ramekins or teacups or small bowls (this is easiest if you pour it into a pitcher, or the measuring cup you already used) and cool to room temperature. Chill the ramekins, covered, at least 4 hours or overnight (I put them all on a small, rimmed baking sheet for easy covering -- I use a single piece of plastic wrap -- and easy transport to and from the fridge.)
Serve them right out their dishes with berries or berry sauce (I like to add just enough sugar -- maybe a tablespoon -- to sliced strawberries to get them to juice up). Or, be fancy and unmold the panna cotta: dip the ramekins, 1 at a time, into a bowl of hot water for 3 seconds; run a thin knife around the edge of each ramekin and invert the ramekin onto the center of a small plate (see Recipe Note below).