Whisk to combine flour and salt in a bowl. In a separate bowl, beat butter with an electric mixer on medium-high speed until creamy, about 2 minutes. Add sugar gradually, beating until mixture is pale and fluffy, about 3 minutes. Beat in extract, then egg. Reduce speed to low, and add one-third flour mixture. Gradually add remaining flour mixture, beating just until blended. Halve dough and shape into disks; wrap each in plastic, and chill 2 hours or up to 1 day.
Preheat oven to 350°F. Roll about 1 tablespoon of chilled dough between your palms to form 1 1/4-inch- to 1 1/2-inch-long oval shapes. Slightly elongate one side to form face. Gently pinch bridge of nose to form eye sockets. With a paring knife, make 2 small slits at top of each shape, for placement of ears. (I didn't do this step. Instead, I just broke a sliced almond in half and stuck each half onto the dough.) Place 2 sliced almonds into slits. Place shapes on parchment-lined baking sheets, spacing 2 inches apart.
Bake, rotating sheets halfway through until cookies are light golden brown on bottom and around edges, and tips of ears are golden brown, about 20 minutes. (I did not rotate my sheets and the cookies came out fine.) Transfer sheets to wire racks. Let cookies cool completely on wire racks.
To make the faces, I made some chocolate ganache and put it in a freezer Ziploc bag and cut a tiny hole at the bottom and then piped eyes and a nose for each mouse.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.