Of course, you can't make chocolate fudge brownies without chocolate. Using a chef's knife, coarsely chop chocolate bars or squares on a cutting board. Chopped chocolate melts smoothly and evenly and won't scorch. Some recipes call for cocoa powder in lieu of actual chocolate—either option will yield delicious brownies.
Place the chopped chocolate in a medium saucepan. Cut up the butter and add it to the saucepan with the chocolate. Stir over low heat until the chocolate and butter are melted and the mixture is smooth. Remove the saucepan from the heat and let the chocolate mixture cool. This will serve as the base for your brownie recipe.
Add the sugar to the cooled chocolate-and-butter mixture. Stir with a wooden spoon until the sugar is completely incorporated.
Add the eggs to the chocolate mixture one at a time. Stir vigorously with a wooden spoon after each addition, until the eggs are completely incorporated into the chocolate mixture. (Fun fact: Eggs provide structure and texture to your brownies, which is why boxed brownies often still need them.) After adding eggs, stir in the vanilla.
In a separate bowl, stir together the flour and baking soda. Add the flour mixture to the chocolate mixture all at once. This is another step where you have some flexibility: Perhaps you eat a gluten-free diet or you'd rather use whole wheat flour instead of all-purpose. Maybe you want to try out a flour substitute like coconut flour or almond flour; in that case, do some research before making a 1:1 swap, since the amount could differ from all-purpose flour.
Your brownies are almost ready to bake. Gently stir the batter until the flour is moistened. Use a heavy-duty rubber spatula to scrape the sides and bottom of the saucepan.If desired, stir in your choice of mix-ins, such as chocolate pieces, chopped nuts, or mint chips. This is another opportunity for flexibility. You can change the mix-ins every time you bake to alter the taste and texture of your brownies without changing the base recipe.
Grease your baking pan or line it with foil for easy removal. Spread the batter in the prepared brownie baking pan. Bake brownies as directed in the recipe, and cool them completely in the pan on a wire rack. Most brownies bake at 350°F for 25 to 35 minutes. If you aren't sure if your batch is done, don't rely on the toothpick test—since fudgy brownies are so moist, this method won't work. If the brownies look overly gooey, use an oven thermometer to make sure your oven temp is accurate