Preheat the oven to 350 degrees F.
Line a metal 9x9-inch baking pan with parchment paper and spray with cooking or baking spray. Set aside. Crack eggs into a glass measuring cup and beat well with a fork.
Microwave chocolate in glass measuring cup on 30 second intervals. Stir with a spoon until melted and smooth.
Melt butter in a glass measuring cup in the microwave. (about 30 seconds to 1 minute)
In a large mixing bowl add sugar, whisked eggs, vanilla extract and combine with an electric hand mixer or a stand mixer.
Combine the melted butter and melted chocolate, stir with a whisk or rubber spatula to combine until smooth.
Scrape the chocolate and butter mixture into the sugar and eggs mixture. Use a rubber spatula to scrape all of the chocolate mixture into the bowl. Beat with an electric hand mixer or use a stand mixer to combine.
Sift flour into a small bowl. Add salt. Whisk flour into the chocolate sugar mixture using a whisk or an electric hand mixer to combine everything until smooth.
Fold in crushed Heath bar pieces with a rubber spatula.
Pour the brownie batter into a prepared 9x9 inch baking pan. (Metal pan preferred lined with parchment paper and sprayed with cooking or baking spray.) Use a rubber spatula to spread the brownie batter evenly into the baking pan.
Bake in a preheated 350-degree F oven for about 55-60 minutes, or when a toothpick when inserted comes out with only a few crumbs. Rotate the baking pan 180 degrees about half way through baking process.
Let cool for about 1 hour before removing from the baking pan. Let cool completely before slicing.