The recipe is:
1/2 cup butter 8 oz semi-sweet chocolate 3/4 cup granulated sugar 1/4 cup light brown sugar 3 large eggs 1 tsp vanilla extract 1/2 cup + 2 tbsp all-purpose flour 2 tbsp unsweetened cocoa powder 1/4 tsp salt
Melt the butter and chocolate over low heat. Let cool slightly for about 10 minutes. Whisk in the sugars. Add the eggs, one at a time, and then whisk in the vanilla. Fold in flour, cocoa, and salt. Bake at 350 for 35 minutes.
I followed this recipe to the letter, but when I added in the flour, the butter starred separating out of the batter. I still followed through with the recipe, and the flavour turned out fine. However, the brownies were very crumbly and the edges very crunchy. I've never had this happen before with brownies. What could cause the butter to separate out?