Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans with butter or non-stick spray, and line the bottoms with parchment paper to ensure easy removal after baking.

In a medium-sized bowl, sift together the all-purpose flour, baking powder, salt, cinnamon, and nutmeg. Set aside.

In a large mixing bowl, beat the softened unsalted butter, granulated sugar, and brown sugar together using an electric mixer on medium speed. Beat for 2-3 minutes until the mixture becomes light and fluffy.

Add the eggs, one at a time, beating well after each addition. Then add the apple butter and continue to beat until fully combined.

Gradually add the dry ingredients mixture to the wet ingredients in 2-3 batches, alternating with the milk. Start and finish with the dry ingredients. Mix just until combined; be careful not to overmix.

Divide the batter evenly between the two prepared cake pans. Smooth the tops with a spatula. Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then transfer them to a cooling rack to cool completely.

While the cakes are cooling, prepare the buttercream. Beat the softened unsalted butter in a large bowl until creamy and smooth. Gradually add the powdered sugar, brown sugar, and molasses, beating on low speed until smooth. Once combined, increase the speed to medium and beat for an additional 2-3 minutes until fluffy.

If the frosting is too thick, add 2-3 tablespoons of heavy cream, one tablespoon at a time, until you achieve a smooth, spreadable consistency. Add a pinch of salt to balance the sweetness.

Once the cakes have completely cooled, place the first layer on a serving plate. Spread a layer of brown sugar buttercream over the top. Place the second cake layer on top and frost the entire cake with the remaining buttercream.

Slice and serve your delicious Apple Butter Cake with Brown Sugar Buttercream. Enjoy!