In a large bowl, combine sliced plums, chopped apples, brown sugar, Triple Sec, cornstarch, almond extract and allspice. Spoon mixture into a 10" cast iron skillet or heavy baking dish.
Make Biscuit Topping:
Add flour to a bowl and grate the cold butter over it. Rub the cold butter into the flour using your fingers or a pastry cutter until the mixture looks like coarse sand.
Gently stir in the whipping cream until mixture is just moistened.
Assemble the Cobbler
Use your hands to gently mound the dough in small islands on top of the fruit mixture in the cast iron skillet. Sprinkle coarse sugar on top.
Bake in the middle rack of the oven for about 45 minutes. If the top is browning quickly, move the cobbler to the bottom rack for the last 5-10 minutes.
Serve warm with ice cream, whipped cream or English custard.
Notes
Choosing Your Plums: Blue European plums are generally better for baking than red plums because they are firmer and less juicy, which helps prevent baked goods from becoming overly soggy. However, I like that red plums are juicier and provide a softer texture for this recipe. Use whichever is your favourite!Adjusting the Sweetness and Acidity: If you plums are very sweet, pair them with a tangy apple (like a Northern Spy). If your plums are tangy, pair them with a sweet apple (like a Honeycrisp).Making the Topping: When you get to the part where you rub the butter into the flour mixture, try to work quickly. You don't want the heat of your hands to melt the butter, and you don't want to overwork the dough. Alternatively, you could use a pastry cutter or a fork to work the butter into the flour.How to Store Leftover Cobbler:
Make sure your cobbler is completely cool before storing.
To store leftover cobbler, cover it tightly with plastic wrap or place it in an airtight container. It should stay fresh in the refrigerator for up to 4 days.
To reheat, warm individual portions in the microwave or place on a heatproof dish in a 350°F (175°C) oven until heated through.
I prefer not to freeze cobbler, as I have found this makes the topping soggy.