Coat an 8 in square pan (or similar pan) with 1 tbsp. butter.
Melt chocolate with remaining 7 tbsps butter (in double boiler so it does not scald).
Meanwhile, beat eggs in medium mixing bowl at high speed 1 minute.
Gradually add sugar to eggs, beating constantly.
Continue beating until mixture is pale yellow and reaches consistancy of soft-peaked whipped cream, 4-5 mins.
Reduce mixer speed to medium; beat chocolate mixture and vanilla into egg mixture until thoroughly blended.
Add flour to chocolate mixture; beat at low speed just until flour is absorbed.
Stir in nuts if desired using a spoon.
Spoon batter into prepared pan.
Bake until cake tester or wooden toothpick comes out clean, about 30 mins.
Cool completely (do not refrigerate).
Cut into 16 squares.
Dust with powdered sugar if desired just before serving.
For extra-chewy texture, cover brownies and let stand at room temperature overnight.
Thermal Control
Standard cakes rely on chemical leaveners, but dense chocolate squares depend entirely on whipped eggs for structure. Melting semisweet chocolate requires gentle indirect heat using a double boiler to prevent scorching the milk solids. Beating whole eggs with granulated sugar for four to five minutes incorporates microscopic air cells that expand during baking at 375 degrees Fahrenheit.
The Chemistry of Retrogradation
Resting baked goods overnight changes starch molecules significantly through a process called retrogradation. Starch recrystallization occurs during this eight-hour room temperature window, causing moisture to redistribute evenly across the crumb. Covering the pan prevents surface drying while allowing interior fats to firm up into a denser, chewier bite.
Nutritional Quality Shifts
Freshly shelled nuts provide aromatic volatile oils that older, commercially packaged counterparts lose during prolonged shelf storage. Substituting freshly chopped walnuts maintains higher polyunsaturated fat content, contributing distinct bitterness that cuts through 38 grams of sugar.