Ready, Set, Go!
Preheat oven to 350 degrees F.
For the crumble, mix 1/2 cup flour, 4 tbsp melted unsalted butter, 1/4 cup sugar and 1/4 tsp sea salt. Set aside.
For the cake, cut up one pound of rhubarb into one inch pieces. Mix with 3/4 cup sugar. Let sit for two minutes, then stir.
Grease a 9" cake pan with butter and drop pieces of unsalted butter on bottom of pan, equalling 4 tbsp.
Whisk together 1 and 1/4 cups of flour with 1 and 1/2 tsp baking powder and 1 and 1/2 tsp salt. In a separate bowl, mix 1.5 sticks of softened unsalted butter and 1 and 3/4 cups of sugar until it looks fluffy, about two minutes. Beat in zest of one lemon and 1 tbsp of fresh lemon juice. Then beat in two eggs, one at a time. Mixture should look silky at this point.
Beat in flour mixture divided into three parts, alternating with sour cream. In total, one cup of sour cream is used. By the end of mixing, the batter should look like this:
Dump the rhubarb mixture into your cake pan and spread evenly. Then pour batter evenly over rhubarb. Finish by sprinkling the crumble on top.
Bake for one hour. Crumble mixture should lightly brown. Remove from oven, let stand for ten minutes.
At the end of ten minutes, run a knife around edge to loosen it then flip it over onto a plate. Voila! The smell is ridiculous- you have been warned.