Preheat the oven to 375°F (180°C).
Prepare the filling: Hull the strawberries and halve any larger ones. Pit and slice the plums into wedges.
Place the strawberries and plums in a 11x7 inch baking dish. Add the vanilla, brown sugar, and orange zest, tossing together to combine.
Make the topping: Whisk the flour, almond flour, sugar, baking powder, and salt together in a medium bowl.
Add the cold, cubed butter to the dry ingredients. Use your hands or a pastry cutter to rub or cut the butter into the flour mixture, breaking up the cubes until they are the size of small peas. If using your hands, work quickly so the heat from your fingers does not melt the butter. Keeping the pieces of butter cold and intact is what creates that flaky, biscuit structure.
If using a food processor, pulse the mixture in short bursts just until the butter breaks down into small pieces. You will know the mixture is ready when it looks like a coarse meal with visible, cold bits of butter distributed evenly throughout.
Add about 2 tablespoons of ice water and use a fork to gently toss the mixture and water together. The goal is to hydrate the flour without overworking the dough. It should look slightly shaggy and uneven, but hold together when you pinch a piece between your fingers.
If the mixture is too dry to clump together, add more ice water one tablespoon at a time. Mix just until it holds its shape.
Using a tablespoon, dollop big spoonfuls of dough on top of the fruit filling.
Bake for 30-45 minutes, or until bubbling and the biscuit topping is golden and cooked through. Serve with vanilla ice cream, if desired.