In the stand mixer bowl, with the whisk attachment, beat the egg yolks with the sugar until the mixture whitens.
Add the softened butter, then change the whisk to the flat beater.
Add the flour, fleur de sel, and baking powder, which have been sifted beforehand, and mix until a dough forms.

Press the dough into the bottom of a 9-inch (23 cm) springform pan, then refrigerate for 1 hour.

In the meantime, peel the apples and rhubarb, then cut them into small pieces.
Put everything in a large saucepan with the maple syrup and sugar.
Let it rest for 15 minutes, allowing juice to form.

Cook for 30 minutes or until the apples and rhubarb are well cooked.
Blend the mixture with an immersion blender or regular blender, then let it cool.

Preheat the oven to 350 F (180 C).
Bake the Breton sablé for 20 minutes.

Upon removal from the oven, cover the warm Breton sablé with white chocolate chips.
Wait 2 minutes, then, using a spatula, spread the white chocolate over the top of the Breton sablé.

Let it cool completely.

Assembly: