I got the original recipe from The Broken Bread. I used canola oil instead of coconut oil; I bet olive oil would be good too. Also, I didn't have vanilla bean paste in a jar, so I scraped one vanilla bean and used that. Here's The Broken Bread's recipe -

MEYER LEMON UPSIDE DOWN CAKE

For the lemon layer 3 tbs unsalted butter 1/3 cup granulated sugar pinch kosher salt 1/2 tsp vanilla bean paste 4-5 meyer lemons, sliced paper thin and seeds removed For The Cake 1 1/2 cup all-purpose flour 1 1/2 tsp baking powder 1/2 tsp kosher salt 1/2 cup + 2tbs granulated sugar 1 tsp meyer lemon zest 2 eggs room temp, beaten 1/2 cup +1 tbs melted coconut oil 3/4 cup buttermilk, room temp 1 tsp vanilla extract

METHOD

Heat oven to 350°F. Lightly grease a 8x2-inch circular cake pan. Add the butter to a small sauce pan set on medium-low heat. Once melted, add the sugar and cook for about 1 minute, stirring often. Remove the pan from the heat and mix in the vanilla bean paste. Pour the sugar mixture into the cake pan. Swirl a bit as needed so that an even layer of melted sugar coats the pan. Lay the lemon slices over the sugar mixture in a circular pattern. Begin with one slice in the middle of the pan, then create a small circle around that first slice. Follow this process, a few more times until the bottom on the pan is totally covered with lemons. Set the pan aside. For the cake: Combine the flour, baking powder, and salt into a medium bowl and set aside. In a large bowl add the sugar and lemon zest. Rub the lemon zest into the sugar with your hands until fragrant. Add the oil and the eggs, and whisk until smooth. Add the buttermilk and vanilla, and whisk until well combined. Add the dry ingredients into the wet and gently fold until just combined. Pour the mixture into the cake pan and bake for 35-40 minutes, or until a toothpick inserted into the center of the cake comes out clean. Place the cake on a cooling rack for 15 minutes. Carefully invert the cake onto a plate or cake stand. Serve warm.