Slice biscuits in half and set aside. In a medium bowl, mash strawberries with a potato masher or the back of a fork. Stir in 4 tablespoons sugar.
In the bowl of a stand mixer fitted with the whisk attachment, whip heavy cream, mascarpone, remaining 2 tablespoons sugar and vanilla extract until peaks form.
Assemble stacks by layering half a mini biscuit with a scoop of strawberry filling, a dollop of whipped cream, the other half of the biscuit, another scoop of strawberry filling and another dollop of whipped cream.
Garnish with a small strawberry, if desired. Repeat with remaining ingredients.