Preheat the oven to 350°F (175°C). Thoroughly grease and flour a 10–12 cup Bundt pan, making sure to get into every groove. Alternatively, use baking spray containing flour.

Peel, core, and dice the Granny Smith apples into approximately ½-inch pieces. Set aside.

In a small bowl, combine the brown sugar, cinnamon, melted butter, and a pinch of salt. Mix until the mixture resembles damp cinnamon sugar. Set aside.

In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, nutmeg, and cloves.

In a large mixing bowl, beat the softened butter, oil, and brown sugar for 2–3 minutes, until well combined and creamy.

Add the eggs one at a time, beating well after each addition. Mix in the vanilla.

Add the sour cream and mix until incorporated.

Add the dry ingredients to the wet ingredients and mix on low speed just until combined. Do not overmix.

Using a spatula, gently fold in the diced Granny Smith apples until evenly distributed throughout the batter.

Spoon approximately ⅓ of the batter into the prepared Bundt pan and spread it evenly.

Sprinkle half of the cinnamon swirl mixture evenly over the batter, keeping it slightly away from the outside and inside edges of the pan.

Add another ⅓ of the cake batter and carefully spread it over the cinnamon mixture.

Sprinkle with the remaining cinnamon swirl, again avoiding the edges.

Cover with the remaining cake batter and gently smooth the top.

Tap the pan gently on the counter a few times to settle the batter and release any large air pockets.

Bake at 350°F for approximately 50–65 minutes, beginning to check at 50 minutes. Insert a toothpick or thin skewer into a thick portion of the cake, avoiding the apple pieces and cinnamon swirl. The cake is ready when it comes out without wet batter; a few moist crumbs are fine.

Place the cake on a wire rack and allow it to cool in the pan for 15 minutes.

Carefully invert the cake onto the wire rack or serving plate. Allow it to cool completely before glazing.

Melt the butter in a small saucepan over medium heat. Continue cooking, swirling occasionally, until the butter becomes golden brown, develops toasted brown flecks, and smells nutty, approximately 2–4 minutes.

Immediately remove from the heat and allow it to cool for 1–2 minutes.

Whisk in the powdered sugar, vanilla, salt, and 3 tablespoons milk.

Add additional milk 1 teaspoon at a time until the glaze is thick but pourable. It should slowly ribbon off the whisk rather than run like a thin icing.

Pour the brown butter glaze over the completely cooled Bundt cake, allowing it to naturally drip down the sides.

Let the glaze set for about 15–20 minutes, then slice and serve.