Preheat your oven to 350°F (175°C). In your 9-inch round cake pan, pour in the melted butter and sprinkle the brown sugar evenly over the top.
Position the sliced nectarines in a circular pattern over the brown sugar.
In a large mixing bowl, combine the buttermilk, eggs, and sugar. Whisk them together until well blended and smooth.
In another bowl, whisk together the flour, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, stirring until just combined.
Gently pour the batter over the arranged nectarines in the pan, spreading it evenly with a rubber spatula.
Place the cake in the preheated oven and bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, allow the cake to cool in the pan for about 10 minutes. Then, carefully run a knife around the edges to loosen it. Place a serving plate over the pan and quickly flip it over.
