Yes. You can freeze an unbaked apple tart. Do not brush with egg wash, or sprinkle with sugar. Instead, place the unbaked tart on a lined baking tray and freeze until solid. Wrap the frozen tart in parchment paper and slip it into a zip-top freezer bag and press out the air. Freeze up to 1 month. When ready to enjoy, brush the edges with egg wash and sprinkle with white sparkling sugar. Bake from frozen.