Mix butter and sugar in a stand mixer fitted with a paddle attachment at medium speed until well combined and creamy.

Add the eggs and vanilla and combine.

Whisk flour, salt, and cornstarch together in a separate bowl.

Add the flour mixture to the wet ingredients little by little. Mix at low speed until well combined.

Form the dough into a ball and wrap it with plastic wrap.

Chill the dough in the refrigerator for 30 minutes.

Move the oven rack to the upper-middle and lower-middle positions.

Preheat the oven to 350 degrees F.

Spray two baking sheets with nonstick cooking spray or line with parchment paper.

Cut the dough using a 2 ½ inch round cookie cutter or biscuit cutter.

Place the cut dough rounds on the prepared baking sheets.

Bake for 12 to 15 minutes or until the edges are golden, rotating the pans halfway through baking.

Let the cookies cool for 5 minutes, then transfer them to a wire rack to cool completely for at least an hour. They must be completely cool before you add the icing.

In a stand mixer fitted with the whisk attachment, whisk powdered sugar, flavor extract, water, and meringue powder until it’s fluffy and has peaks in it on medium to high speed. This could take anywhere from 4 to 5 minutes.

Check the consistency of your icing. If it's too thick, add more water, a very small amount at a time.

You should aim for a medium consistency. (Medium royal icing is slightly thinner than piping icing.)

Once you have the consistency you want, place it into a piping bag fitted with a small round tip.

Seal the piping bag with a knot or with a rubber band.

Outline each cookie with icing, and continue making a spiral inwards.

Then immediately, with a toothpick or offset spatula, spread the icing evenly and smooth it out.

Place the eyes on the cookie.

Repeat with the remaining cookies.

Allow the icing to set before adding the mummy lines over each cookie.

To make the mummy lines, drizzle each cookie with a bit of icing to make it look like the mummy wrapping. Be careful not to cover the eyes.

Let the icing dry completely.

Serve.