For the cake

1. Preheat oven to 350°F/177°C.  Grease and flour three 8-inch round cake pans.  Line with parchment paper and set aside.
2. In a medium bowl, sift the flour, baking powder, baking soda, and salt.  Set aside.
3. In a large bowl using a hand-held mixer or stand mixer fitted with the paddle attachment, beat together the butter and sugar on medium-high speed until smooth and creamy, 4-5 minutes.  Scrape down the sides of the bowl as needed.  Beat in eggs, one at a time, until combined.  Scrape down the sides of the bowl and beat in the sour cream and vanilla until combined.  With the mixer on low speed and in three parts, alternately add the dry ingredients and the milk to the batter, beginning and ending with the dry ingredients.  Beat until just combined.  Fold in the mini chocolate chips.
4. Divide the batter evenly between the cake pans and spread with a small offset spatula.
5. Bake in preheated oven for 30-35 minutes or until a toothpick inserted in the center comes out clean.
6. Allow the cakes to cool completely in the pans set on a wire rack before frosting.

For the buttercream

1. In a large bowl using a hand-held mixer or stand mixer fitted with the paddle attachment, cream together the butter and brown sugar for 2-3 minutes.
2. Add the powdered sugar and flour and mix on low speed until incorporated.  Pour in the milk and mix until combined.  Add the vanilla and salt and increase mixer to high speed.  Beat for 3 minutes until light and airy.

To assemble

1. Remove the cakes from the pans and peel off the parchment paper.  Using a large serrated knife, slice a thin layer off each cake to create a leveled surface.
2. Place one layer of cake onto your cake turntable, cake stand, or serving dish.  Spread an even layer of buttercream.  Top with a second layer and repeat another layer of buttercream.  Add your final layer of cake.
3. Using an icing spatula, spread the remaining buttercream on the top and sides of your cake.
4. Refrigerate your cake while you prep your ganache.

For the chocolate ganache

1. In a medium heatproof bowl, add your chocolate and heavy cream.  Place over a small saucepan filled with an inch of boiling water.
2. Cook the chocolate and heavy cream until smooth stirring occasionally.
3. Remove from heat and check for a pourable, but not runny consistency.  If too runny, allow it to cool until the correct consistency.
4. Pour the chocolate ganache into a pastry bag and cut a 1/8 - 1/4-inch off the tip.  If you don't have a pastry bag, then you can spoon the ganache over the cake.  Begin from the center of the cake and work your way out.  Apply a thin, even layer to the top leaving about 1/2-inch border around the edges.  Wait about 10 seconds to allow any extra spreading.  Continue with the edges allowing ganache to drip down the sides every so often.