Preheat the oven to 350 degrees.
Place the apple slices in a medium bowl and sprinkle with the lemon juice and toss. Set aside.
In another medium bowl, melt the butter in the microwave. Add the brown sugar and stir to combine. Scrape the butter-sugar mixture into the bottom of the pan and spread into an even layer.
Lay the apples evenly over the butter-sugar mixture. Set the pan aside.
In a 1-cup measuring cup, mix the buttermilk, vanilla, and oil. Set aside.
In another medium bowl, blend your dry ingredients (flour through salt) and set aside.
In a mixer bowl, add the 4 ounces of room temperature butter. Mix on medium for 2 minutes to lighten. Slowly add the sugar and mix for another minute.
Add the eggs, one at a time, blending well after each addition.
Turn the mixer to low and slowly add about a third of the dry ingredients. Before fully incorporated, add half the buttermilk mixture. Again, just before the mixture is completely blended, add another third of the flour mixture. Alternating like this, add the last half of the buttermilk, then the last third of the flour mixture. Keeping the mixer on low, combine thoroughly, only a few seconds.
Using a silicone spatula, scrape all the batter into the prepared pan. (See notes – I like to use the baking strips that wrap around the exterior of the pan to help with evenly distributing the heat while the cake is in the oven.)
Bake the cake for about 50 minutes. Begin checking the cake at 45 minutes, in case your oven bakes on the hotter side. Keep checking every 4 to 5 minutes until done. Once a toothpick inserted in the center comes out mostly clean, pull from the oven (remove the baking strips if using) and allow to cool for 20 minutes.
Here’s the magic…. Place your cake plate/stand on top of the warm cake and flip over so that cake comes out onto the cake plate/stand with the gorgeous apples on top and the syrupy, brown sugar oozing down the sides. It’s best to allow the cake to cool slightly, but you can (and I sure have!) eat a slice while still warm. It’s also good at room temperature. This cake is so lovely and aromatic!