Remove the stems and chop the strawberries with a knife.
Cook and Cool the Strawberries. Combine the chopped strawberries and granulated sugar in a small saucepan over medium-low heat. Simmer for 5 to 10 minutes until the berries break down and become soft and syrupy.
Puree the mixture with an immersion blender or standard blender until completely smooth. Press the mixture through a fine-mesh sieve to remove the seeds if you want a silky texture. Cool the puree completely to room temperature, then chill it in the refrigerator before using.
Whip the Mascarpone and Cream. Place the chilled mascarpone, cold heavy cream, powdered sugar, and vanilla extract into a large bowl. Beat on low speed for 30 seconds to break up the cheese and combine the ingredients. Increase the speed to medium-high and whip until the mixture forms thick, stiff peaks.Watch closely and stop mixing as soon as it holds its shape so the cream does not over-whip.
Fold and Chill. Pour the chilled strawberry puree into the whipped mascarpone cream.
Fold gently with a rubber spatula, cutting down the center and sweeping up the sides. Stop mixing as soon as the color is uniform and pink to keep the texture light.
Spoon or pipe the mousse into individual serving glasses or dessert bowls.
Refrigerate for at least 2 hours to let the dessert set and firm up before serving