Melt together the butter and chocolate in a small saucepan over very low heat, stirring to mix.
Remove from heat when almost melted (do not scorch).
Preheat your oven to 300F.
Fill a 9x13-inch roasting pan or casserole halfway with water and place it on the center shelf of the oven.
Lightly grease the sides and bottom of a 9x5-inch loaf pan, and dust with 1 teaspoon of flour; and cut out a square of waxed paper to fit the bottom of the pan; place paper in the bottom of pan and set aside.
Place sugar, eggs and remaining 1 teaspoon of flour into the bowl of an electric mixer and beat on high for about 2 minutes.
Pour in the chocolate, and beat another 15-30 seconds, until it is mixed well.
Pour the batter into the prepared loaf pan and set the loaf pan in the center of the casserole dish half-filled with water (in the oven).
Bake for approximately 75 minutes or until a light crust forms and a toothpick can be removed clean.
Cool the cake in the loaf pan on a wire rack for approximately 30 minutes, or until it cools down to room temp.
Cover pan and chill in the refrigerator for 4 hours or until set.
Serve garnished with powdered sugar or fresh raspberries and store unused portions in the refrigerator.