Using a stainless saucepan (using stainless will allow you to easily see the color of the caramel as it browns), add your granulated sugar and place over medium heat.
Stir the sugar as it begins to melt. It will clump up and you'll think it's not right but just keep stirring. All the sugar will eventually melt.
Caramel can burn very quickly, so as soon as it starts to caramelize watch it carefully. You want it to be somewhere between medium and dark amber. Err on the side of too light rather too dark as you cannot fix a burnt caramel. As soon as it reaches the right color, remove from the heat.
Carefully pour in your heavy cream and continually whisk. Be very careful! The mixture will bubble up a lot, but just keep mixing until the caramel is smooth again.
Add in your butter and salt and mix until melted. Let your caramel cool in the pan for a few minutes and then pour into a glass jar or measuring cup to let cool.
Allow your caramel to cool for about an hour before pouring it over your brownies. Neither the brownies or caramel will have cooled completely, which is fine. Make sure there is a good layer where no brownie is peeking through and it reaches the edges.
Place your brownies in the fridge to let the caramel set and the brownies finish cooling.
When ready to eat (1-2 hours of chilling in the fridge at least), remove and sprinkle with flaky sea salt. Cut into 16 squares (or 9 for larger brownies) and top each square with a pecan half. Enjoy!