Preheat the oven to 350°F. Line a 9x13 baking dish with parchment paper and spray with cooking spray, set aside.
Place the cut butter into a large pot or dutch oven, and begin to melt the butter over medium-low heat.
Break up the chocolate bar into squares and add them to the pot, stirring occasionally, melt the chocolate with the butter until smooth.
Take off the heat and whisk in the sugar until smooth. Add the eggs one at a time and whisk them in fully before adding the next.
Whisk in the vanilla and salt. Add the flour and stir it in until fully combined with no dry patches.
Pour into the prepared baking dish. Bake for 35-38 minutes until a toothpick inserted into the center comes out mostly clean.
Place on a wire rack to cool completely.
Once the brownies are cool, make the topping. Place the sugar, evaporated milk, butter, and egg yolks into a medium-sized saucepot.
Place over medium-low heat and stir together. Stir occasionally until the butter has melted.
Bring the mixture to a simmer while still stirring occasionally so nothing sticks to the bottom. Once it hits a simmer and thickens slightly take it off the heat, for about 12 minutes.
Add the coconut, pecans, and vanilla. Stir it in to combine. Continue to stir until it becomes thickened and spreadable, about 5 minutes.
Pour the frosting on top of the brownies and smooth it out. Let it cool completely.
Cut into bars and drizzle with melted chocolate if using, serve immediately.