Preheat the oven to 350 F (175 C). Line an 8-inch square metal baking pan with parchment paper, leaving enough overhang on the sides to lift the brownies out after cooling.
Add 1 ¼ cups granulated sugar, ½ cup melted and cooled unsalted butter, 1 large egg, 1 large egg yolk, and 1 teaspoon vanilla extract to a large mixing bowl. Whisk until well combined.
Sift ¾ cup all-purpose flour, ⅓ cup unsweetened cocoa powder, and ½ teaspoon sea salt into the bowl. Use a rubber spatula to gently fold the dry ingredients into the wet ingredients just until combined and no streaks of flour remain. (Note 1)
Spread the batter evenly in the prepared pan. Bake for 20–23 minutes, until the top looks set and the center no longer appears wet or glossy. Take care not to overbake.
Remove the brownies from the oven and let them cool completely in the pan, about 1 hour. (Note 2)
Use the parchment overhang to lift the cooled brownie slab out of the pan. Cut into 12 bars with a sharp knife.
Add ½ cup white chocolate chips and 1 ½ tablespoons coconut oil to a microwave-safe bowl. Microwave in 15-second intervals, stirring well after each interval, until the chocolate is almost completely melted. Stop heating while a few chips remain and continue stirring until the residual heat melts them. (Note 3)
Use a spoon or fork to drizzle the melted white chocolate back and forth over the brownies. The lines do not need to be perfectly even; a mix of thicker and thinner lines creates the wrapped mummy look.
Place 2 candy eyes on each brownie, using a small dot of melted white chocolate to hold each one in place. Let the white chocolate set before serving.