Preheat your oven to 375℉.
To make the biscuits, in a large bowl combine the flour, baking powder, salt, and cardamom. Add in the butter and work with your hands or a pastry cutter until it's pea-sized. Pour in the buttermilk and mix until just combined.
Dump out onto a floured surface and work gently with your hands (not too much!) to a rectangle. Fold the two sides inward on top of each other, then roll out to 1 inch thick. Cut into square pieces 1 ½ inches big. Put into the fridge until ready to bake.
For the filling, in your 10" cast iron or baking dish, combine the quartered strawberries, raspberry jam, lemon zest, granulated sugar, corn starch, and salt. Mix to combine.
Take the biscuits out of the fridge and snuggle them on top of the strawberry mixture. They should all be touching!
In a small bowl, whisk together the egg and a dash of water. Brush on top of the biscuits and top them with a few tbsp of turbinado sugar.
Bake for 50-55 minutes until the berries are bubbling and the biscuits nice and golden brown.
Enjoy warm with vanilla ice cream!