In a medium bowl add the all-purpose flour and salt. Set aside.

In a large mixing bowl, add the softened unsalted butter and granulated sugar. Using a hand mixer, on medium speed, cream together the butter and sugar for 2-3 minutes or until smooth.

To the butter mixture add the egg and clear vanilla flavoring. Beat again for 1-2 minutes or until fully incorporated.

Add the dry ingredients to the bowl of wet ingredients and beat on low speed until it comes together to form a thick, and smooth, dough. Scrape the sides and bottom of the bowl with a rubber spatula to ensure that all the dry ingredients are fully incorporated and the dough is well combined.

Cover the bowl of cookie dough with plastic wrap and refrigerate for 30- 60 minutes.

Preheat the oven to 350* F. Line two large baking sheets with parchment paper and set aside.

Using a 1 tablespoon cookie scoop, scoop out a level amount of chilled dough and roll it in the palm of your hand to create a smooth ball. Place the rolled ball onto a baking sheet and repeat until all the dough has been rolled and placed onto the two prepared baking sheets. Be sure to leave about 2 inches of space between each dough ball.

Using a small rounded measuring spoon, or your thumb, press an indent into the center of each dough ball that is about ¾ - 1 inch wide. This should flatten your dough ball slightly and the indentation should not go all the way to the bottom of the dough ball. Repeat until all the cookie dough balls are indented.

Bake the cookies for 10-12 minutes or just until lightly golden around the bottom edges.

Remove the thumbprint cookies from the oven and allow them to cool on the pan for 5 minutes before transferring them to a wire rack to cool completely before icing them.

To a large mixing bowl add the sifted powdered sugar, 2 tablespoons whole milk and clear vanilla flavoring. Whisk until smooth. You want a thicker consistency, not a pourable one. Start with the 2 tablespoons of whole milk then add 1 teaspoon at a time (up to 1 tablespoon) to get desired consistency.

If you are making a single icing color, you will add the gel food coloring of your choice, starting with 2-3 drops, until you reach your desired color. If making multiple colors see tips below. Stir the gel food coloring into the icing until no streaks remain and the color is uniform.

Using a small spoon, or transferring the colored icing to a small piping bag with the end cut off, fill each of the indentations of the cooled thumbprint cookies. Be careful not to overfill the indentations with the icing.

Allow the iced thumbprint cookies to sit at room temperature to allow the icing to firm up before placing onto a serving plate or adding to a container for storage.