Heat in 30 second increments, stirring between each, until fully melted.
Whisk in the sugar until dissolved.
1 ⅓ cups granulated white sugar
Whisk in the heavy cream.
2 Tablespoons heavy cream
Add in the eggs and vanilla and continue whisking until fully combined.
3 large eggs, 2 teaspoons vanilla extract
Add in the cocoa powder, flour, salt, and baking powder. Use a spatula to fold in until no traces of flour are left.
½ cup unsweetened cocoa powder, ½ cup all purpose flour, ¾ teaspoon salt, ½ teaspoon baking powder
Stir in the chocolate chunks until evenly distributed.
½ cup chocolate chunks
Pour the brownie batter into the prepared baking dish and sprinkle additional chocolate chunks over the top.
Bake for 40 minutes. The center should be set and a toothpick in the center should come out mostly clean with some moist crumbs. You don't want to overbake them but they may need up to 50 minutes depending on your pan and oven.
Once done, remove from the oven, let cool for approximately 10 minutes, lift the brownies from the pan and use a plastic knife to cut into 9-12 pieces.
Notes
Semi-sweet chocolate bar or chips can be used, but I recommend using a bar. I tested with a Ghirardelli bar and a Baker's semi-sweet bar.
I used Ghirardelli unsweetened cocoa powder. Dark chocolate cocoa powder will also work well.
I used Nestle semi-sweet chocolate chunks.
Bake times can vary based on type of pan. I used an 8x8 metal pan.
A 9x9 pan can be used, the brownies will be slightly thinner and bake time will be 30-40 minutes.
Store leftovers covered at room temperature for up to 5 days.
Baked brownies can be frozen. Wrap tightly individually and store in a freezer bag for up to 3 months. Thaw at room temperature.