Very good for weekend brunch / snacking. Included in this cookbook per request from Andrew.
3 tablespoon firm margarine
1 cup milk
Heat oven to 350. Prepare Streusel by cutting the margarine into the other ingredients and mixing until crumbly. Beat cake ingredients (except blueberries) in large mixer bowl on low speed 30 seconds. Beat on med speed, scraping bowl occasionally, 2 min. Spread half of the batter in greased 9x13 pan, or 9x9 pan; sprinkle with half of the streusel and half the blueberries (if desired). Top with remaining batter; sprinkle with remaining streusel and blueberries (if desired). Bake 9x13 pan about 35 min; 9x9 pan about 45 min (until wooden pick inserted in center comes out clean).