Step 1: Preheat your oven to 350°F (175°C).
Step 2: Line a 9x9 inch baking pan with parchment paper.
Step 3: Melt the salted butter and unsweetened chocolate together in a medium saucepan over low heat.
Step 4: In a mixing bowl, whisk together the eggs, granulated sugar, and vanilla until well combined. Gradually add in the melted chocolate mixture.
Step 5: In another bowl, sift together the all-purpose flour and salt. Fold into the wet mixture.
Step 6: Gently fold in the chopped walnuts.
Step 7: Pour the batter into the prepared baking pan and smooth the top. Bake for 20-25 minutes.
Step 8: Allow to cool in the pan for 10 minutes, then lift out and cool completely before slicing.
