Place the flour, sugar and salt in a food processor and pulse to mix.
Add the butter to flour mixture and pulse until the mixture resembles bread crumbs (do not over process).
Add the egg yolk, vinegar, vanilla and a teaspoon of the iced water and pulse until the dough just starts to come together.
If needed, add a splash more water and pulse until the dough comes together.
Put the dough on lightly floured surface and gently pat it together.
Flatten the dough into a disk, wrap in plastic and chill for about 2 hours.
Remove the dough from the fridge and let it warm up a bit to make it easier to roll out.
Roll the dough into a large rectangle and use a small side plate (about 15cm in diameter) to cut out 6 – 8 disks and place onto 2 baking sheets lined with baking paper.
Preheat the oven to 200 degrees °C.
Mix the almonds, sugar and zest together and sprinkle onto the rolled out disks leaving a 2cm edge.
Arrange the apple slices onto the pastry.
While rotating the tart, fold the border of exposed dough up and inwards, crimping and pushing it up against the fruit.
Brush the border with the egg wash.
Bake for 25 mins until the crust is well browned.
Remove from the oven, gently remove from the baking paper and place onto a cooling rack to prevent the bottom of going soggy.
While the galettes bake make the tahini butterscotch.
Combine the cream and butter in a small saucepan, and cook over a low heat, stirring occasionally, until the butter melts.
Add the tahini, and sugar and whisk until the tahini has dissolved.
Bring to the boil, reduce the heat and cook for another 10 mins, stirring constantly until thickened and shiny.
Serve the galettes warm, with a spoonful of butterscotch and some vanilla ice cream.