Preheat an oven to 180c (350f). Butter the bundt cake pan with room temperature butter and flour to prevent the cake from sticking to the pan.
In a big mixing bowl, add the room temperature butter, sugar, vanilla extract, kosher salt, and mix with an electric hand mixer until it's creamy.
Add the room temperature eggs, and mix until combined.
Add the sour cream, oil, peach puree, and mix well.
In a medium sized bowl, add the flour and baking powder. Mix with a whisk until combined.
Add ½ of the flour mixture and mix until almost combined.
Add the rest of the flour mixture and the buttermilk and mix until just combined and there are no lumps of flour visible.
In a small mixing bowl, add the melted butter, brown sugar, cinnamon, and nutmeg, and mix until combined.
Pour the cinnamon butter mixture and arrange the peach slices on top of the butter mixture.
Carefully, top the peaches with the cake batter and smooth the top out with a spatula.
Bake in a 180c (350f) oven for about an hour or until a toothpick inserted into the cake comes out clean.
Allow the cake to cool to room temperature before flipping the cake. Top the pan with a plate, flip the cake and tap the cake pan to release the cake from the pan.