Preheat your oven to 350F, grease, and line an 8X8 inch pan. Set it aside.
Prepare a double boiler. Pour half a cup of water into a small saucepan and bring it to a boil. Let the water simmer on low heat. Place the chocolate chunks and butter in a bowl over the simmering water, ensuring the water does not touch the bottom of the bowl. Stir occasionally until the butter and chocolate are melted and smooth.
6 ounce Semi-sweet Chocolate, ⅓ cup+1tbsp Butter
Set the mixer on a whisk attachment or use a hand mixer. Whisk the eggs with two sugars for 3-5 minutes. Be patient with this step if you want to achieve that shiny, cracked top. Add the vanilla extract and mix.
2 Eggs, 2 teaspoon Vanilla extract, ¾ cup Granulated sugar, ¼ cup Brown sugar
Add the melted butter/ chocolate mixture to the egg mixture. Mix well.
Sift the flour, salt, and cocoa powder into a separate bowl. Add this to the batter, and use a rubber spatula to fold the dry ingredients into the batter. Do not overmix the batter.
2 tablespoon Cocoa powder, ½ cup All-purpose flour, ¼ teaspoon Salt
Pour half of the batter into the lined pan and bake. Place about 12 Reese's Thins on top of the batter, and pour the remaining batter on top of the thins.
16-20 Reese's Thins
Bake the brownies for 20-25 minutes. After 20 minutes, check the brownies by inserting an insert into the center of the batch. The insert should come out with a semi-moist batter sticking to it. Immediately after removing them from the oven, place chopped Reese's Thins on top of the baked brownies.