Preheat oven to 375F hi-fan.
Roux is almost equal parts flour + butter, slightly excess of flour
Pull out roux early in the day
Pie dough 85 g each, roll out + chill
About 1 apple per tart. Peel and chop thin slice for apple. Set aside.
Scatter coarse sugar on table and roll chilled dough round into it until it's about 8" (20 cm) diameter. Roll the edges loosely into a crumpled tube — do not over pinch or flatten. It helps to keep the dough chilled so that it stands up.
Put a few lumps of soft roux in a container and work it smooth with a spoon handle. Add lemon juice a few drops at a time until tasty.
Add any remaining lemon juice to the fruit
Add roux paste, sugar and cinnamon to coat the fruit.
Spoon the fruit into prepared tart shell.
Sprinkle coarse sugar on top. No egg wash needed.
Bake 375F in oven until the pies are golden. Rotate the sheet pan once during last third of baking time.
If there is a lot of juice that bubbled out, grander tarts to a clean pan with parchment paper.