Preheat oven to 375 degrees.
Spray a bundt pan well with baking spray with flour. Set aside.
In a small mixing bowl, combine butter, sugar and chopped walnuts. Mix together until crumbly.
Drop into prepared bundt pan. Make sure the bottom of the pan is covered with the nuts. Do not press into pan. Place in the refrigerator.
Combine flour, baking soda and salt in a mixing bowl. Set aside.
If you do not have buttermilk, pour one tablespoon of lemon juice (bottled or freshly squeezed) or vinegar in a one cup measuring cup. Fill the rest of the cup with milk. Stir and set aside for 5 minutes. Let curdle. (this is what buttermilk is supposed to do).
In a stand mixer with the paddle attachment or with a hand mixer, mix butter, brown sugar and vanilla extract until light and fluffy.
Drop in eggs, one at a time, beating well after each addition.
Add about 1/3 of the dry ingredients and beat. Add 1/2 cup of the buttermilk and beat. Keep repeating, alternating between the dry and wet, end with the dry.
Fold in mini-chocolate chips. Spoon on top of the nut mixture. Gently tap the pan on your work surface to allow for air bubbles to escape.
Bake for 40 minutes or until a toothpick inserted in the center of the cake comes out mostly clean.
Remove from oven. Let cool for about 5-10 minutes. Gently tap the pan to loosen the cake from the edges.
Place cooling rack on top of the pan. Flip over and let cake finish cooling on the wire rack.
Serve with or without ice cream.
Enjoy!