01 -
Blend blackberries until smooth, strain if desired, measure 6 ounces.
02 -
Heat oven to 350°F, grease 8-inch pan and line with parchment.
03 -
Beat butter, sugar and dry ingredients until fluffy, add egg whites gradually.
04 -
Alternate adding flour and blackberry puree in thirds.
05 -
Pour into pan, bake 30 minutes until puffed.
06 -
Cool in pan 1 hour, then turn out and cool completely.