Preheat oven to 350F. Also, prep your baking pan or muffin tray.
Combine the flour, baking powder and baking soda with the salt.
In a bowl, whisk the butter, white sugar and brown sugar together until the mixture is a well combined pale color. I usually whisk for about 5 minutes.
Add in the eggs, one at a time, and whisk for about 2 minutes after each addition.
Add in the flour mixture in 3-4 batches alternating wiht buttermilk. Incorporate each addition barely before adding the next. Do not over mix.
Add in the chocolate and walnut pieces if using. Mix together until well combined. Divide the batter into a muffin pan or the baking pan.
Place in the oven and bake until a knife inserted comes out clean. Using my deep jumbo muffin tin, it takes about 40-45 minutes. For smaller muffin tin, I suggest you start checking at 20 minutes mark.
