Gluten Free Rhubarb Upside Down Cake

First, trim the rhubarb stalks to make sure that they fit snugly into a 9-inch (23cm) cake pan. I recommend doing a test run, where you arrange them on the bottom of the pan before you line it with parchment/baking paper. That way, you’ll be confident that all the rhubarb stalks fit snugly on the bottom of the pan, without having to do any additional trimming later on.When it comes to the rhubarb topping, you can make the “pattern” on top as simple or as complex as you want. I just cut the rhubarb stalks to size and arranged them in a simple parallel fashion (see blog post for photos).

Adjust the oven rack to the middle position and pre-heat the oven to 350ºF (180ºC). Lightly butter a 9-inch (23cm) round cake pan and line its bottom with a round of parchment/baking paper. Generously butter the parchment/baking paper as well.Tip: Don't use a springform pan, as some of the rhubarb juices could leak out during baking.

Sprinkle the sugar in an even layer on the bottom of the prepared cake pan.

Arrange the rhubarb stalks on top of the sugar so that they completely cover the bottom of the pan. Make sure that they're packed together as tightly as possible (that’ll prevent the batter from getting underneath them and it’ll give you the prettiest end result).Set aside until needed.

In a large bowl, cream together the sugar, butter and vanilla until pale and fluffy. You can do this by hand with a large balloon whisk, using a stand mixer fitted with the paddle attachment or a hand mixer fitted with the double beaters.

Add the eggs, one at a time, mixing well after each addition, until well combined.Tip: It's very important that your eggs are at room temperature and that you add them one at a time. This way, you'll maintain the emulsion of the butter as much as possible. If you forgot to take your eggs out of the fridge, place them in warm water for 5-10 minutes before using them.

In a separate bowl, whisk together the gluten free flour blend, almond flour, baking powder, xanthan gum and salt.

Add half of the dry ingredients to the butter-sugar mixture, and whisk well to combine. Add the yoghurt and whisk until smooth. Finally, add the rest of the dry ingredients and whisk well until you get a smooth cake batter with no flour clumps.Tip: This alternating way of adding dry and wet ingredients helps to maintain the emulsion of the butter in the cake batter as much as possible. When alternating dry and wet ingredients, make sure to always end with the dry.

Add the chopped rhubarb and mix well until it's evenly distributed throughout the batter.

Dollop the batter on top of the rhubarb layer and smooth it out into an even layer.

Bake at 350ºF (180ºC) for about 55-60 minutes or until the cake is golden brown on top, well risen and an inserted toothpick or cake tester comes out clean. If the cake starts browning too much or too quickly, cover it with a sheet of aluminium foil (shiny side up) and continue baking until done.

Allow the cake to cool in the cake pan for 10-15 minutes, then carefully invert it onto a large plate while it's still hot. (Run a knife or a small offset spatula along the edges of the cake to loosen it from the pan if necessary.)Tip: Don’t cool it for longer than that, otherwise your cake can end up sticking to the baking pan when you try to remove it.

Serve the cake either warm or cooled completely to room temperature. It pairs beautifully with a scoop of vanilla ice cream or a dollop of lightly sweetened vanilla whipped cream.

The rhubarb upside down cake keeps well in a closed container in a cool, dry place for 2-3 days .