I first made this coffee cake nearly 25 years ago, after wrangling the recipe out of one of my coworkers. It was back in the day when I worked in the mortgage industry ... before the real estate crash ... the crash of the '80s. (Now I feel old!) It's been a staple of workplace potlucks and family gatherings ever since.
2 cups flour
1 cup light brown sugar
1/2 cup sugar
1/2 cup oil
1 cup sour milk*
1 teaspoon salt
1 teaspoon soda
1 teaspoon vanilla
3 Heath or Skor candy bars, crushed (but not turned into powder)
Heat oven to 350 degrees. Grease and flour 9X13 cake pan. Combine first four ingredients with pastry blender; save 1/2 cup (not packed!) for later.
Combine all remaining ingredients except candy and mix well by hand; pour into pan. Sprinkle evenly with reserved topping then crushed candy bars. Bake for 30 minutes. Cut into serving pieces with serrated knife immediately after removing from oven (cake must be cut before the candy topping hardens). Cool completely before serving.
*To make sour milk, pour 1 tablespoon cider vinegar into a measuring cup; add milk to equal 1 cup; let stand for 3-5 minutes.