Preheat oven to 350 degrees. Lightly spray a 9" x 1 1/2 " round cake pan with cooking spray.
Chop the rhubarb into 1/2" chunks. In a large bowl, toss the rhubarb with 1 cup sugar and 1/4 cup flour until the pieces are well coated. Spread the rhubarb mix over the bottom of the prepared cake pan.
In another bowl, beat the ricotta cheese with the egg until smooth and creamy. Add the almond extract and 1/4 cup sugar and mix well. Add 1 cup flour and the baking powder and mix well. The batter will be thick, almost like biscuit dough.
Spread the dough over the rhubarb in the pan, making sure it goes all the way to the edge. Be careful not to let the juice from the fruit mix into the dough.
Put the cake in the oven with a piece of foil under the pan to catch any drips that might bubble over. Bake at 350 degrees for 45 minutes.
While the cake is baking, coarsely chop the macadamia nuts. Melt the butter in a small bowl. Add the brown sugar, chopped nuts, and cornflake crumbs and toss until blended and crumbly.
Remove the cake from the oven and allow to cool for 30 minutes. Put a serving plate over the pan and invert onto the plate. Tap the bottom of the pan to release the cake onto the plate (you can tell that the cake is out and on the plate when the pan sounds hollow when you tap it).
Sprinkle the nut topping over the fruit (which is now the top of the cake) and press lightly.
Allow the cake to cool before serving. Serve at room temperature or chilled.