In a bowl, combine butter, cake mix, eggs, blueberries, 1/3 cup white chocolate chips and pecans.
Butter 7-by-11-inch pan and spread mixture evenly into pan. Bake 30-35 minutes. Let cool then melt remaining white chocolate chips and drizzle over bars.
Tip: If melted white chocolate chips are too thick, add a little oil before drizzling.