I love a good upside down cake, no matter what kind of fruit you use. My family always uses pineapple but when I saw how beautiful all of the citrus looked at the grocery store I decided to play with the ingredients! The result was delicious. The cake is so flavorful because of all the fresh citrus zest that you put into the batter. Make sure you don’t skip this step! —Blakely
Butter an 8 inch round cake pan and line the bottom with parchment paper to ensure it doesn't stick.
In a saucepan over medium high heat melt the butter and brown sugar while you prepare the citrus.
With a sharp knife slice the ends of oranges and grapefruit. Following curve of fruit, cut away peel, removing as much white pith as possible. Once all the white pith is gone, slice them into rounds and remove any seeds. Once the sugar and butter is melted pour it into the bottom of the cake pan and spread it evenly. Arrange the sliced citrus on the bottom and then set it aside while you make the cake batter.
In a bowl with an electric mixer cream together the butter, brown sugar, and granulated sugar until smooth.
Add the egg, egg yolk, and citrus zest and give it another mix.
Add the milk, sour cream, and fresh lemon juice and mix it together again
To the wet ingredients add the flour, baking powder, baking soda, ground nutmeg, and salt. Mix until combined, scraping down the sides, and then pour it over the citrus.
Put it into oven and let it bake for 50-60 minutes. I put a toothpick in the middle of the cake around 50 minutes to see if it would come clean or not. If it comes out clean then it is ready! Take it out and let it cool slightly for about 5 minutes. Run a knife along the edges to make sure it doesn't stick when inverting. Put your cake stand or plate on the bottom of the cake and flip it over. Remove the parchment paper and voila! A delicious and very impressive cake.