• Preheat the oven to 325 °F or 350 °F.

Caramel

• In the cast iron pan (or saucepan) add the first measure of granulated sugar and set over medium-low flame. Allow the sugar to melt. Swirl it every minute until a light amber colour is achieved. Set this aside. If you are using a saucepan, transfer the caramel to a lined and greased cake pan.
  150 g granulated sugar
• Wash and trim the rhubarb to the size of the pan. Arrange the rhubarb in one even layer on top of the caramel.
  450 g trimmed rhubarb

Upsidedown Cake

• In the bowl of a stand mixer, or in a mixing bowl with an electric mixer, cream together the butter and both sugars. Cream until a fluffy consistency forms.
  85 g butter, 120 g dark brown sugar, 50 g granulated sugar
• Add the spices, vanilla, and salt. Mix until the mixture is fragrant.
  1 tsp vanilla extract, ¼ tsp salt, 3 g cinnamon powder, ½ tsp ginger powder, ⅛ tsp clove powder, pinch ground nutmeg
• Slowly add each egg, mixing well between additions and scraping down the sides of the bowl.
  2 lg eggs
• In a bowl, combine the remaining dry ingredients. Add one third of these ingredients to the butter mixture as well as one third of the buttermilk. Fold these in gently until three quarters of the flour and buttermilk are incorporated. Add half of the remaining dry ingredients and half of the remaining buttermilk and fold in to the mixture until three quarters of the flour and buttermilk are mixed in. Finish with the remaining dry ingredients and buttermilk until it is all incorporated.
  8 g baking powder, 120 g buttermilk, 195 g all-purpose flour
• Transfer the batter to the prepared pan with the caramel and rhubarb. Bake the cake for 45 minutes to one hour, until a toothpick inserted comes out with two to three crumbs on it.
• Allow the cake to cool until the pan can be handled but the cake is still warm. Losen the side of the cake. Place a serving platter over the pan and then flip the pan over so the cake falls onto the platter. Serve warm and enjoy with a caramel sauce and a scoop of vanilla ice cream.