Line an 8x8 inch (20x20 cm) or 9x9 inch (23x23 cm) baking pan with foil, parchment paper, or wax paper.

If you are not using chocolate chips, roughly chop the chocolate (900 grams/ 2 pounds) and place it in a medium to large heatproof (or microwavable) bowl.

Add the sweetened condensed milk (792 grams/ 28 ounces), diced butter (56 grams/ ¼ cup), and salt (1 teaspoon) into the bowl.

Choose which method below you will utilize to melt the chocolate.

Setup a double boiler: Fill a medium saucepan with about 2 inches (5 cm) of water. Place on the stove and turn to medium heat and bring the water to a simmer. Turn the heat down to low. Set the bowl over the saucepan of simmering water, making sure that the bowl is not touching the water. If the water is touching the bowl, pour out some of the water.

Use a rubber spatula to stir the mixture as the chocolate begins to melt until you have a smooth texture and all of the chocolate is melted. The mixture will be very thick, almost like a dough.

Place the microwavable bowl of chocolate into the microwave and heat for 45 seconds on high. Stir the mixture thoroughly being sure to scrape the bottom and sides of the bowl. Heat for 30 more seconds and stir the mixture again. Heat in 15 second increments, stirring in between, until the mixture is a smooth consistency. This should take about a 2-4 minutes from start to finish. The mixture will be very thick, almost like a dough.

Spread the fudge into the prepared pan using the back of a spoon, rubber spatula, or offset spatula. Spread until it is evenly spread and smooth on top.

Allow to sit at room temperature for at least 3 hours or in the refrigerator for at least 2 hours to set before cutting. Slice 4 rows by 4 columns to make 16 large squares or 6 rows by 6 columns to make 36 small squares.

The fudge can be stored in an airtight container at room temperature for about 1 week or in the refrigerator for up to 3 weeks.