Grease and flour one 12-cup bundt cake pan, tapping out any excess flour.
Coarsely chop CHUNKS (easily done in food processor, being careful not to over process). Combine CHUNKS with pecan pieces, ¼ cup sugar and cinnamon; set aside.
In large mixing bowl cream together butter and 1¼ cups sugar until light and fluffy.
Add vanilla and eggs, mixing well.
Scrape down sides of the bowl.
In medium mixing bowl sift together flour, cocoa, baking powder, baking soda and salt.
Add dry ingredients, in thirds, to butter mixture, alternately with sour cream, beginning and ending with dry ingredients.
Place half the batter into prepared pan, spreading level.
Top with ½ the pecan mixture.
Repeat with remaining batter and pecan mixture.
Bake 50 to 60 minutes, or until wooden toothpick tests done.