Start by pouring the cold water into a medium-sized bowl. Evenly sprinkle the unflavored gelatin powder over the water. Let it sit undisturbed for 5 to 10 minutes until it softens and blooms.
Gently warm 1 cup of raspberries in a small saucepan over low heat, allowing them to release their juices. Once warm, carefully strain the raspberries through a fine mesh sieve to create a smooth, vibrant puree, discarding any seeds or pulp. Set this beautiful puree aside. Keep the other 1 cup of raspberries chilling in the fridge for your topping later.
In a separate saucepan, combine the heavy cream and 1/4 cup of sweetener. Heat gently, stirring continuously, until the sweetener is completely dissolved. Remove the pan from the heat.
Whisk in the prepared raspberry puree into the warm cream mixture. Then, slowly pour this delicious cream and raspberry mixture into the bowl with the bloomed gelatin, whisking vigorously as you pour. Continue whisking gently until the gelatin is fully dissolved and the mixture is smooth.
Carefully divide the creamy mixture evenly among 6 small glass jars or ramekins. Place them in the refrigerator and chill for at least 2 to 4 hours, or until the panna cottas are beautifully set and firm.
Just before serving, lightly sweeten the remaining chilled fresh raspberries with 1 tablespoon of powdered sweetener. Spoon these sweet berries generously over your now firm panna cottas. Enjoy this elegant, healthy treat! Store any leftovers in the refrigerator.