Preheat your oven to 350° Fahrenheit.
Cream together the butter and sugar.
Add eggs one at a time, mixing until smooth.
In a medium bowl whisk together the flour, baking powder, and salt.
Whisk your milk, yogurt, and extract in a separate jug.
Add ½ of the dry mixture to the butter mixture and mix to combine.
Finish on the rest of the dry mixture.
Thoroughly grease an 8x8 pan with nonstick cooking spray and line with parchment paper (leaving overhang on both sides).
Place the rhubarb pieces along the bottom of the pan in an even layer.
In a medium sauce pan add the sugar and water.
Turn the stove on medium heat, swirling the pan constantly, until the mixture is boiling and it reaches a medium shade of amber.
Pour the bubbling sugar mixture over the rhubarb.
Add the cake batter overtop of the rhubarb and caramel and use an offset spatula to smooth into even layer.
Bake the upside down cake for 35-40 minutes or until the top of the cake is golden brown and springs back to the touch.
When the cake comes out of the oven, run along the sides of the pan with an offset spatula to release the edges.
Let the cake cool for 5 minutes, and then invert it onto a serving plate.
Slice and enjoy!
