Mix butter or oil with one cup of sugar in a bowl of a stand mixer with the paddle attachment until smooth.
Add eggs, pumpkin, buttermilk, and vanilla and mix again until smooth. Turn off mixer.
Add all dry ingredients to the bowl, including the chocolate chips. Allow the chocolate chips to be coated with the flour to help prevent sinking of the chocolate in the cake.
Line the bottom of two 8-inch round cake pans with parchment paper and grease the pans, oruse one 10-inch Springform pan.
Bake at 350 for about 35 minutes for 8-inch pans, or about 45 minutes for 10-inch pan. A toothpick inserted in center of cake should come out witha few moist crumbs attached when done.
Remove from oven and let cool. Invert onto a plate, then turn over again onto a platter to serve, or if using a springform pan, remove the sides when cooled and place on platter.