Crust:

1. In a large bowl, mix flour with sugar, salt, and lavender (if using).
2. Add olive oil in a thin streak while mixing with a fork. Continue mixing until crumbly.
3. Pour water slowly into the crumbly mixture while still mixing with a fork until just absorbed.
4. Remove dough from the bowl; knead with one hand just until you can squeeze the dough into a ball that holds its shape. Once it does, stop kneading, or your dough will be too firm.
5. Place a piece of baking parchment on the work surface; lightly dust with flour. Divide the dough in two halves, place one on the parchment, and roll out to an imperfect circle with a thickness of 1/8 inch. Turn the dough while rolling it out to prevent sticking. Place the dough circle into the fridge for half an hour.
6. Repeat with the other half of the dough.

Filling and Assembly:

1. Preheat oven to 425°F220°C/Gas Mark 7.
2. Slice the plums.
3. In a large bowl, toss plum slices with sugar, salt, flour, and any or all of the optional ingredients until every slice is coated. Let sit for 10 minutes; drain any juices the plums have given.
4. Remove one crust from the fridge.
5. Pile ½ of the plum filling in the center of the circle, spread slightly. Fold the edges over the filling in a somewhat sloppy manner.
6. Brush the edges with egg wash; generously sprinkle with coarse sugar.
7. Repeat with the other dough circle and the remaining filling.
8. Bake for about 40 minutes until the edges are deep golden brown, with no pale spots.
9. Let cool till warm and slice up. Serve topped with a dollop of crème fraiche or a scoop of vanilla ice cream.