Preheat the oven to 350ºF (177ºC). Line an 8" or 9" square baking pan with foil and spray with nonstick spray. Set aside.
In a medium saucepan over medium heat, melt the butter and chopped chocolate, stirring frequently until completely smooth. Allow to cool for about 15 minutes.
Whisk sugar into cooled chocolate mixture until combined. Add the eggs one at a time, whisking after each addition until smooth. Whisk in the vanilla. Add the flour and salt and stir gently until completely combined.
Pour the batter into the prepared pan. Bake brownies for 32-35 minutes or until a toothpick inserted in the center comes out mostly clean. Allow brownies to cool completely before cutting into squares and decorating.
DECORATE THE BROWNIES
When you are ready to decorate the brownies, remove the brownies by lifting the foil overhang straight up. Peel back remaining foil and place brownie block onto a large cutting board.
Using a sharp knife, cut the block horizontally into equal thirds. Cut each third into 6 rectangular pieces. Place individual brownies on a flat surface or baking sheet lined with parchment or wax paper. Set aside.
In a microwave safe bowl, melt the white chocolate by heating in 20 second increments on MEDIUM power, stirring after each time. When the chocolate is smooth, pour into a piping bag (plastic or reusable) fitted with a size 3 or size 5 round piping tip.
Using a zigzag motion, drizzle white chocolate in one direction over the entire length of each mummy. While the chocolate is still wet, add 2 candy eyes. Drizzle white chocolate in the other direction. Allow chocolate to set before serving. Store leftover brownies at room temperature up to 1 week. Undecorated brownies freeze well, up to 3 months. Thaw in refrigerator then decorate.
*Room temperature eggs: these incorporate into batter much more easily than cold eggs, although this is not absolutely necessary.Adapted from homemade fudgy brownies