Preheat the oven to 350°F and line an 8x8 pan with foil and lightly grease. Set aside.
In a medium sized bowl over low heat, melt the butter. Add in the sweetened condensed milk and stir with a whisk. Add in the dark chopped chocolate and continue mixing until everything is smooth and melted. Remove from heat and set aside to cool.
1/2 cup butter, 14 ounces sweetened condensed milk, 3/4 cups dark chocolate
In a large bowl, beat the eggs, egg yolk, and both sugars. Whisk vigorously for 2 minutes until light and airy. There should be bubbles forming. You may also use an electric mixer for this part to save elbow grease!
1/4 cup brown sugar, 1/4 cup white sugar, 2 eggs, 1 egg yolk
Add in the slightly cooled chocolate mixture from earlier and gently fold together using a spatula. Do not overmix!
Add in the flour and unsweetened cocoa powder and continue mixing until no streaks appear.
3/4 cups all-purpose flour, 1/4 cup unsweetened cocoa powder
Toss in the chocolate chips and mix for a few seconds.
1/4 cup dark chocolate chips
Pour into a prepared 8x8 square pan and spread out evenly. Bake for 30-35 minutes or until a toothpick inserted comes out slightly fudgy. Please note: This baking process can take upwards of 50 minutes depending on your oven! If it is wet with batter, continue baking. Start checking your brownies after 30 minutes and check every 5 minutes. Once ready, turn off your oven.
Slightly open the oven door for 10 minutes and allow the hot air to come out. Then completely remove the brownies from the oven and cool on the counter.