Beat the eggs with the sugar with a mixer until whitened.
Mix the flour with vanilla and baking powder, pour in slowly while alternating with the water. Pour everything into a rectangular tray covered with baking paper.
Grate the quince coarsely, stir with the brown sugar and cinnamon. Sprinkle it over the unbaked cake.
Bake at 356°F (180 °C) on the lower element initially. Once swollen, turn on the upper one too.
You can sprinkle with powdered sugar if you like; I didn't because I put extra brown sugar in with the quince and it was plenty sweet.