In a heavy-bottomed saucepan, combine the evaporated milk, 1 cup of sugar, and the lime rind (if using). Stir the mixture well to combine all the ingredients.
Place the saucepan over medium heat. Stir continuously to prevent the sugar from sticking to the bottom and burning.
As the mixture heats up, it will begin to bubble. Once it reaches a gentle boil, reduce the heat to low.
Continue to stir the mixture constantly for about 30 to 40 minutes until it thickens to a creamy consistency.
Once thickened, remove it from the heat and pour the mixture into the prepared baking dish or tray.
Allow the dulce de leche to cool at room temperature for about 1 to 2 hours, then refrigerate for an additional 2 hours until completely set.
Once set, cut the dulce de leche into squares or rectangles and serve immediately or store in an airtight container.