Prep. Get out 6 individual glasses (I used 6-ounce dessert glasses or juice cups). Divide 1 cup strawberry puree between the 6 glasses, about 2 tablespoons + 2 teaspoons per glass (see Notes to soft set the strawberry puree). (TIP: Taste your strawberry puree first, and if it's too tart you can add sugar or whatever sweetener you like to taste.)
Bloom the gelatin. Add the cold water to a small bowl and sprinkle the gelatin on top. Let it sit for a couple minutes without stirring so it can harden. Once it's hardened, mix in the hot water until the gelatin is fully dissolved. Cool to lukewarm.
Mix. While the gelatin blooms, add 1 1/2 cups strawberry puree, the cream cheese, sweetener, cream, and balsamic vinegar to a large bowl. Use a hand-held electric mixer to beat until smooth and creamy. Add the liquified gelatin and mix until well-combined.
Divide and chill. Divide the mixture between the 6 glasses. Cover each glass with plastic wrap and chill until set, about 12 hours.
Enjoy. Serve chilled. Right before serving, add any toppings you like.
Notes
Strawberry Puree: You can use fresh strawberries or frozen (thawed and most of the liquid poured off) strawberries. You'll need about 3 1/2 cups of whole strawberries to get 2 1/2 cups of puree.
To Soft Set the Strawberry Puree: This will give it a texture similar to a soft-set strawberry JELL-O. Add 1 tablespoon cold water to a small bowl, sprinkle 1 teaspoon beef gelatin on top, let it set for 3 minutes, add 1 tablespoon hot water, and stir to dissolve. Cool to lukewarm. Stir the dissolved gelatin into 1 cup of strawberry puree and divide it between the 6 individual serving glasses. Transfer to the fridge for 3 to 4 hours to slightly set before adding the mousse layer on top.
To Get a Fluffy Look (Instead of a Flat Surface) on Top of Your Mousse: You'll need to let it partially set before transferring it to the individual glasses. Once you make it, let it chill in the fridge until it's partially set (about 3 to 4 hours); check it periodically because you want it to be quite thick but still pourable. Use a rubber spatula to gently fold it briefly, and then gently spoon it into the serving glasses.
Storage: Store this mousse covered in the fridge for up to 4 or 5 days.