Step 1: Preheat your oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper, leaving an overhang on two sides.
Step 2: In a medium bowl, whisk together the melted butter and granulated sugar until well combined and smooth.
Step 3: Add the eggs one at a time, whisking well after each addition. Stir in the vanilla extract.
Step 4: In a separate small bowl, whisk together the flour, cocoa powder, baking powder, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing with a spatula or spoon until just combined. Do not overmix.
Step 6: Pour the batter into the prepared baking pan and spread evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs (not wet batter).
Step 7: Let the brownies cool completely in the pan on a wire rack before cutting. This is crucial for fudgy brownies.
Step 8: While brownies cool, prepare the frosting. In a medium bowl, whisk together the powdered sugar, milk (or cream), and vanilla extract until smooth and creamy. If too thick, add more milk a teaspoon at a time. If too thin, add more powdered sugar.
Step 9: Once brownies are cool, lift them from the pan using the parchment paper overhang and cut into 16 squares or rectangles.
Step 10: Transfer the frosting to a piping bag fitted with a small round tip, or a Ziploc bag with a small corner snipped off.
Step 11: Pipe thin, squiggly lines of frosting across each brownie, leaving a small gap near the top for the eyes. Don't worry about perfection; mummies are messy!
Step 12: Carefully place two candy eyes in the gap you left. Pipe a few more lines over the top of the eyes to resemble bandages.
Step 13: Serve immediately or store in an airtight container at room temperature.