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 strawberry juices could leak out during baking.

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

Arrange the halved strawberries on top of the sugar layer, cut side down, packing them as closely together as possible, so that they completely cover the bottom of the pan.You can also cut a few of the strawberries into quarters and/or eights to fill any holes. You really want them to be tightly packed, this will give you the prettiest end result.Set aside until needed.

In a large bowl, whisk together the sugar, eggs, milk, melted butter, oil and vanilla until well combined.

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

Add the dry ingredients to the wet and whisk everything together into a smooth, fairly runny cake batter with no flour clumps.

Pour the batter over the strawberries.

Bake at 350ºF (180ºC) for about 35-40 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 5-10 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 strawberry upside down cake keeps well in a closed container in a cool, dry place for 2-3 days.