Start by preheating your oven to 350°F and lining your baking pan with parchment paper, leaving a little overhang on the sides. This overhang makes it so much easier to lift the brownies out later without wrestling with the pan. I always take an extra thirty seconds here because a well-lined pan saves a lot of frustration once the brownies are baked.
In a bowl, whisk together the melted butter and sugar until it looks glossy, then add in your eggs and vanilla extract. Whisk this mixture well, since this step is actually what gives brownies that shiny, crackly top everyone loves. Fold in the flour, cocoa powder, salt, and baking powder just until combined, being careful not to overmix the batter.
Pour the batter into your prepared pan and smooth the top with a spatula so it bakes evenly. Bake for about 22 to 25 minutes, checking that the top no longer indents when you touch it lightly with a fingertip. A few moist crumbs on a toothpick are totally fine and actually mean your brownies will stay wonderfully fudgy.
Let the brownies cool in the pan for about 15 minutes, then use the parchment overhang to lift them out onto a cutting board. I like popping mine in the fridge for another 10 minutes here, since chilled brownies are so much easier to cut into neat rectangles for your mummy brownie bites.
Once cooled, slice the brownies into rectangles, keeping in mind that longer pieces tend to look more mummy-like than small squares. I usually aim for around 9 to 12 pieces from an 8x8 pan, which gives each mummy plenty of surface area for wrapping.
Melt your white chocolate chips or candy melts in the microwave in short 20-second bursts, stirring between each one so it doesn't scorch. Spoon the melted chocolate into a piping bag or a zip-top bag with a tiny corner snipped off, ready for decorating.
Pipe the white chocolate back and forth across each brownie in a zigzag pattern, leaving a small gap near the top for the eyes. While the chocolate is still soft, press two candy eyeballs into place so they stick as everything sets.