Heat the oven to 350°F and grease a 9-inch cake pan.
Arrange peach slices artistically to cover the bottom of the greased pan (this will be the mosaic for all to see when your cake is fully baked).
Make a dry caramel
Heat 1/2 cup sugar in a medium heavy-bottomed saucepan over medium-high heat. As soon as the sugar starts to melt, use a heatproof spatula to move it constantly around the pan—you want it all to melt and caramelize evenly.
Cook and stir, cook and stir, until the caramel is amber colored, about 3 minutes from when the sugar starts to melt, being careful to never let it burn.
Once the caramel has reached the target color, remove the saucepan from the heat.
Very slowly and very carefully, pour in 2 Tablespoons milk and 1 teaspoon vanilla extract.
The caramel will bubble up and steam; stand away until the steam dissipates.
Use the heatproof spatula to stir the mixture together then drizzle this hot mixture over the peach mosaic in the cake pan.
Make the cake batter
In a mixer, beat the shortening and sugars until light and fluffy.
Add eggs one by one, mixing in between each addition until well combined.
Stream in buttermilk, oil and vanilla extract until well combined.
Add all flour, salt and baking powder and mix until batter is smooth, 1-2 minutes, being careful not to overmix.
Fold in the white chocolate chips.
Pour cake batter over the peaches and bake at 350°F for 40-45 mins until the cake caramelizes, begins to pull back from the sides of the cake pan and, when you insert a toothpick into the center, it comes out clean.
Warm out of the oven, carefully invert the hot cake pan onto a plate or cake dish so the bottom peach brilliance becomes the top. (If any peaches became stubborn and stayed in the pan, just remove them gently and transfer them over to the top of the cake where they belong. There will be indentations so it will be easy!).
Cool before slicing and serving.
The flavors of this cake continue to meld brilliantly on day 2-3-4 so don’t be shy about baking ahead or eating a slice a few days after baking!