Place rack in center of the oven and preheat to 350 F. Lightly grease the loaf pan (5x3 inches 2 cup capacity) Line with a strip of aluminum foil to fit down the length and up the short sides with enough extra lengthy to extend over the edges by about 1 1/2 inches. Lightly grease the foil, and set the pan aside.
2
Place the butter and unsweetened chocolate in a medium-size microwave safe bowl, and microwave on medium power until the chocolate is soft and the butter is melted, about 1 minute. Stir until the chocolate is smooth. Add the sugar and whisk well. Then add the beaten egg and vanilla, and whisk until well blended. Add the flour and salt and whisk well. Spread the batter evenly in the prepared loaf pan.
3
Bake until a toothpick inserted in center comes out with moist crumbs attached, 28-30 minutes. The top will appear dry and will be starting to shrink from the edges of the pan. Do not overcook.
4
Remove the loaf pan from the oven, place it on a wire rack, and let the brownies cook completely in the pan. Use the edges of the foil to lift the brownies out of the pan. Remove the foil and cut the brownies into 3 bars.