Hull and wash the strawberries.
Place them in a blender and purée until completely smooth. For an extra-silky texture, press the purée through a medium-fine sieve to remove the seeds.
Stir 1 cup (200g) of the sugar into the purée and set aside.
In a small saucepan, sprinkle the gelatin over the cold water and let it sit for 5 minutes to soften, or 'bloom'.
Place the saucepan over low heat and warm gently, stirring constantly, until the gelatin is completely dissolved.
Do not let it boil.
Add the remaining 0. 5 cup (100g) of sugar and continue to stir over low heat until the liquid is clear.
Remove the gelatin mixture from the heat and stir it into the strawberry purée.
Transfer the mixture to the refrigerator to cool until it just begins to thicken to the consistency of raw egg whites.
Check it every 10 minutes, as it can set quickly once it starts to cool.
While the strawberry mixture chills, whip the heavy cream in a separate bowl until it forms fairly stiff peaks.
In another clean bowl, beat the egg whites with a pinch of salt until they form stiff, glossy peaks.
Once the strawberry purée has started to thicken, remove it from the fridge. Immediately stir in the Triple Sec or curaçao. Gently fold in the whipped cream using a large spatula, followed by the beaten egg whites, until just combined. Be careful not to overmix and deflate the mixture.
Carefully spoon the mousse into a lightly oiled 6-cup charlotte mold or into 8-10 individual serving dishes.
Place in the freezer for at least 4 to 6 hours, or until firm.
To serve, unmold the charlotte onto a platter or serve in the individual dishes. If the mousse is frozen solid, let it sit at room temperature for 15-20 minutes to soften slightly.
Garnish generously with fresh strawberries before serving.