For the berry mixture: In a medium bowl, combine the raspberries and strawberries, granulated sugar, cornstarch and vanilla. Stir and set aside.
For the crisp: Butter an 8-inch square baking dish. In a large bowl (or food processor), combine the butter pieces, flour, oats, granulated sugar, brown sugar, pecans and salt. Cut together with a pastry cutter (or pulse in the food processor) until the mixture resembles coarse crumbs.
Press half of the crisp mixture into the prepared baking dish. Top with the berry mixture, then sprinkle the remaining crisp over the top. Bake until the topping is golden brown, about 45 minutes. Allow to sit for 10 minutes before serving.
For the whipped cream: Add the cream and granulated sugar to the bowl of a mixer and whip until soft peaks form.
Scoop out the crisp with a spoon and top with sweetened whipped cream