Mix dry ingredients. Using a pastry blender, cut in butter until pea-sized crumbs. Mix in buttermilk and flavoring until combined. Chill for at least a half hour. Remove from the refrigerator and roll into a circle on a lightly floured surface
Bring quince ingredients to a simmer on low heat and cook just long enough to soften. Pour off water and cool.
Layer quince on top of the galette circle. Drizzle with a 1/3 c. maple syrup and fold edges over. Brush with an egg wash (1 egg whisked with 1 T. of milk). Bake at 375 for 25-30 minutes or until golden.