In a medium bowl, mix the butter and cream cheese with an electric mixer. Add the flour and blend until mixed. Press the dough into miniature muffin cups or tartlet shells, making thin shells. Prick the bottom with a fork and refrigerate for 30 min.
Preheat oven to 350º. Bake the shells for 22-30 minutes or until golden brown. Cool completely. Remove each shell and set on wire racks.
In a medium saucepan, boil the cranberries, sugar and water, stirring constantly, until mixture comes to a full boil and berries begin to pop. Remove pan from heat. Stir the cornstarch and Grand Mariner together until the cornstarch is dissolved, then stir into the cranberry mixture. Return the pan to the heat and cook, stirring constantly, until the mixture comes to a full boil and thickens. Remove from the heat and cool to room temperature.
Spoon the cranberry filling into the tart shells and serve.