For the RHUBARB: Wash, peel and cut the rhubarb stalks in pieces. Put them in a bowl, and sprinkle them with 1 teaspoon of white sugar or your preferred granulated sweetener. Let them sit for about 20 minutes.
For the simple one-bowl VANILLA BATTER: Preheat the oven to 360°F/180°C. Place all the dry ingredients for the cake base in a mixing bowl and combine, add the wet ingredients and whisk until it's a smooth batter.
For the STREUSEL: Put the cold butter, all-purpose flour and sugar in a bowl, mix and knead with your hands until crumbly.
ASSEMBLE and BAKE: Oil the baking pan lightly and pour in the cake batter. Drain the rhubarb and spread the pieces evenly onto the cake better. Sprinkle the crumble on top. Bake it in the oven for about about 25 minutes. When the crumble is nice and golden, your cake is ready.