Wash the rhubarb stalks. Cut them into small pieces about 1 to 2 cm thick. Place them in a colander over a deep plate.
Add the brown sugar and mix to coat. Let it macerate for 1 to 2 hours: the excess rhubarb juice will run into the plate, removing the excess acidity.
Preheat the oven to 180 ° traditional heat.
Mix the oatmeal, flour, baking powder, brown sugar, and salt. Then add the melted butter and vanilla extract.
Mix with a spatula until you obtain coarse pieces of crumble (it's a little wet, that's normal).
In a 26cm round ceramic mold like mine, or a rectangular mold of equivalent volume (ceramic for better cooking), place the pieces of rhubarb without their juice.
Sprinkle the crumble dough on top, crumbling it roughly. Keep a free border without dough on the sides of the mold (to check the cooking of the fruit in the oven).
Bake for around 45 minutes (this varies greatly depending on the ovens and molds used). The crumble should be slightly golden, and the fruit will “bubble” (bubble) around the edges of the mold.
Leave to cool before enjoying, plain or with a scoop of vanilla ice cream...
Notes
Once cooked, the rhubarb crumble can be stored in the refrigerator for up to 5 days, covered with cling film or in an airtight container.