►Heat oven to 350°F. Butter an 11x7 baking dish.
►CRANBERRY APPLE FILLING: Combine frozen cranberries, apples, brown sugar, cornstarch, orange juice, zest, cinnamon and salt in a large bowl.
►OATMEAL CRISP: Combine oats, brown sugar, flour, salt and cinnamon in another bowl. Add butter and use your hands to incorporate into the oat mixture, rolling it between your fingers into pea-sized pieces.
►Pour cranberry filling into baking pan in an even layer. Distribute oatmeal topping evenly over the filling. Place on middle rack of oven and bake for 1 hour 15 minutes, or until filling is bubbling and topping is golden brown. Cool for at least 5 minutes before serving.
►MASCARPONE TOPPING: Whip mascarpone and Grand Mariner together until fluffy in a mixer or by hand. Put a dollop of mascarpone on top of each serving.