Cut the rhubarb to fit your cake pan. This takes a bit of trial and error. I like to line the rhubarb up in a row and place the cake pan on top to get an idea of where to trim. Some stalks will be long enough to cut into 2 pieces to use. I can’t emphasize enough how much rhubarb differs in size. I like to fit in as many rows of rhubarb as the cake pan will fit, often putting a piece in the pan only to take out and time a bit more to fit snuggly. Take the rhubarb out and set aside, in a row so you know what order to put the pieces back in.
Melt the butter on the stove and add the brown sugar, cardamom, ginger and salt. Mix and pour this sugar mixture into the cake pan, the line the rhubarb you just trimmed and set aside on top.
In a food processor, finely grind pistachios. Change the blade to the dough blade and add flour, baking powder, and salt; pulse to combine. Add butter in chunks and sugar and beat in processor, beat in beat in eggs, one at a time, then add the flour and beat until combined (stopping to scrape sides down so that all the batter gets mixed). Add orange juice and zest, vanilla, cardamom, and the yogurt. Keep beating until it’s all combined.
Transfer batter to pan, on top of rhubarb stalks, and smooth top.
Bake in oven for 1 hr and 10min.
Cool the cake for 5-10min then run a small sharp knife around edges. Place a plate on top of the cake pan and invert. Slowly lift the cake pan away.
I prefer the cake warm with fresh whipped cream or ice cream but it can also be served at room temperature, as is.
Leftovers can be stored in an airtight container at room temperature for up to 3 days.