Preheat the oven to 350 degrees F (180 degrees C) and grease a 13x9-inch pan.
Melt the Butter (1/2 cup) and the Semi-Sweet Chocolate Chips (1/2 cup) together in a saucepan over low heat and set aside to cool for 15 minutes.
Add the Egg (2), Granulated Sugar (1 cup), and Vanilla (1 teaspoon) to the mixture in the saucepan, and mix until smooth.
Sift the All-Purpose Flour (2/3 cup) and Baking Soda (1/4 teaspoon) together in a separate bowl and add to the chocolate mixture. Combine until it's a smooth batter.
Pour mixture into the greased pan and spread across the whole pan evenly. Place in the preheated oven for 15-20 minutes, remove, and let cool.
The edges of the brownie might have risen- with a sharp knife, cut those edges down so that the brownie is completely level.
Place about one inch of water in a saucepan and let it come to a slow simmer. In a glass or metal bowl, combine the
Semi-Sweet Chocolate Chips (2 1/2 cup), Sweetened Condensed Milk (1 can), Ground Cinnamon (1 1/2 teaspoon), Vanilla Extract (1 teaspoon) and Butter (3 tablespoon).
Place the bowl on top of the simmering water and fold the ingredients with a spatula until it's completely melted together. This shouldn't be rushed and should take around 15 minutes to completely melt.
Pour the fudge over the brownies. The brownies can still be warm but not hot. Smooth with the back of a spoon and make swirls.
Place in the fridge for 1-2 hours to set.
Sprinkle brownies with Sea Salt Flakes (to taste) and Ground Cinnamon (to taste). Slide a warm knife around the outside edge of the brownies, then cut into small squares.