Preheat the oven to 375°.
Wash the fruit and cut the plums in half and slice the peaches. Remove the pit or stones from all the fruit.
Combine the fruit in a bowl with the sugar, cinnamon and orange liquor and pour into a large 3 to 4 quart casserole or souffle dish.
In a mixing bowl combine the flour, sugar, baking powder, and salt. After the dry ingredients are thoroughly blended, add the buttermilk, 1/2 cup heavy cream, and cold butter in quick succession, combining only briefly, to leave the mixture as lumpy as possible.
Pour this lumpy dough onto a lightly floured board and flatten gently with a rolling pin into a shape approximately 1-inch thick and just large enough to cover the top of the fruit in the dish completely.
Top the fruit with the dough and pull the edges towards the dish so that the fruit is enclosed. Brush the dough with melted butter, sprinkle the top with sugar and place the casserole into the oven and bake for 20 to 25 minutes, or until the pastry top is nicely browned.
Whip the heavy cream with confectioners sugar and vanilla and serve with the cobbler.
Servings: 6 to 8