To make the pastry, add flour to bowl of a food processor fitted with a steel blade. Cut butter into 1/4-inch slices and add to flour. Pulse until butter is about the size of kidney beans. If you don't have a food processor you can cut the butter into the flour with a pastry blender or other cutting tool.
In large bowl, dissolve yeast in warm water. Let stand 5 minutes. Stir in cream, salt, eggs and sugar. Turn the flour-butter mixture into liquid ingredients and mix using a rubber spatula until the dry ingredients are just moistened. Cover with plastic wrap and refrigerate 4 hours, or overnight (preferred) or up to 4 days.
To make the filling, toss cherries, apples, both sugars and cinnamon in medium bowl. Cover and allow mixture to stand at room temperature while you prepare the pastry.
Turn dough out onto a lightly floured work surface. Dust dough with flour. Roll out to make a 16x20-inch rectangle. Fold into thirds making three layers. Turn dough and roll out again. Fold again into thirds. Refrigerate 30 minutes.
Preheat oven to 400 degrees Farenheit. On a lightly floured surface, roll chilled pastry to 1/4-inch thickness. Trim edges to square and cut as many 5x5-inch squares from pastry as possible. Re-roll dough scraps and cut more squares.
Place about 2 tablespoons of filling in center of each square. Combine egg and water in small bowl. Using a pastry brush, lightly coat edges of each square with egg wash. Pull one corner over the mixture to meet the opposite corner to form a triangle. Use the tines of a fork to seal the edges.
Place the pastries on parchment-lined baking sheets. Brush with egg wash and sprinkle with additional granulated sugar. Bake the turnovers 18-20 minutes, or until pastries are golden brown. Serve warm.