To bake in a conventional oven, pre-heat to 375°F and bake on the bottom rack, 30-40 minutes.
Know someone who would enjoy this recipe? Why not share it with them.
Mix dry ingredients in large bowl, reserve 2 Tbsp dry mixture to thicken filling. Cut in butter, using two forks or a pastry blender. Leave large lumps of butter visible. Whisk egg and water together; reserve 1 Tbsp to use as egg wash. Add remainder to dry mix, tossing together loosely with the pastry blender and by hand. As dough comes together, form into a ball and place on a floured surface.
For the Filling
Preheat BBQ to its highest setting, all burners. Oil a 12 inch oven-proof skillet: a pizza pan or parchment-lined baking sheet will also work.
Slice top & bottom off each apple; quarter and slice the core from each piece. Thinly slice each quarter across the grain. In the same mixing bowl, toss apples, lemon juice, sugar, reserved dry mix, and cinnamon.
Roll out pastry to a size 4-5 inches larger than the skillet. Try to get the crust thinner than an ordinary pie crust, an eighth inch or less. Patch any tears with a piece from the perimeter. Roll the crust over your rolling pin and lay it across an oiled cast iron skillet. Scatter the corn flakes in the middle of the dough and arrange apples over the corn flakes. Roughly fold/pinch/crimp the edges over the filling leaving the centre of the galette uncovered. Brush the top pastry with the reserved egg wash
Turn one burner of heated BBQ completely off and place skillet in that position. Close the lid: the working burner(s) should be able to maintain a temperature of 350-400°F. At the 30-minute mark, use a spatula to check for browning. Add another 10 minutes cooking time if necessary and/or move the skillet to the live burner for 3-5 minutes. Cool briefly and serve.