DirectionsMelt chocolate and butter together in a double boiler and allow to cool slightly.
In a large bowl, whisk eggs, salt, lemon zest, sugar and vanilla.
Whisk in chocolate mixture slowly.
Fold in flour, then blueberries.
Pour batter into greased 9x13 inch baking pan, bake for 40 minutes at 325 degrees.
Let cool before cutting to prevent too much breakage.