Adapted from
Ready for Dessert by David Lebovitz
You can use salted or unsalted butter for these brownies. If you use unsalted butter and want to add some salt, use 1/8 teaspoon fine sea salt. I also like to add 2 to 3 tablespoons of roasted cocoa nibs along with the nuts for added chocolaty crunch.
Use very low heat for melting the chocolate and butter. A good trick is to add the butter to the pan first, which melts faster than the chocolate, so you don’t burn the chocolate. You can use a flame-tamer if you’re concerned but I always melt it right over the lowest heat possible and never have had any problems.