Preheat oven to 375. Place 2 light colored baking sheets in the fridge or freezer, if you have space.*
Make the dough. In a large bowl or stand mixer, beat 1 cup butter until completely smooth and there are no lumps. If you have a stand mixer, use cold butter. If you are using a hand mixer, you will have to let the butter soften for a few minutes before you start beating. Make sure to scrape down the sides and bottom of the bowl halfway through.
Add 1 cup sugar and 1/2 teaspoon kosher salt (use a little less if using table salt). Beat well for 1-2 minutes until light and fluffy, scraping the sides and bottom of the bowl.
Add 1 large egg and 1 teaspoon almond extract. Beat until incorporated.
Add gel food coloring to the dough at this point if you are planning to use it. Mix well. Remember that you are still adding flour after this, so add enough gel to make a bit of a deeper color than what you want for the final dough. Keep in mind also that gel food coloring intensifies with time.
Spoon and level 2 and 1/2 cups flour into the dough. Beat until JUST combined, scraping the sides and bottom as necessary. Once you get to the point that you don't see streaks of flour anymore, stop beating and leave it alone. You don't want to over mix the dough or your spritz cookies will turn out tough.
Press the cookies. Read the instructions on your cookie press to get it all set up. Put the metal disc in the bottom that is the shape that you want to press. Take a handful of room temperature dough, use your hands to shape it into a cylinder, and feed it into the cookie press. Add it all the way to the top. Screw in the top of the press.
Press the cookies onto the chilled light-colored baking sheets. These cookies do not spread hardly at all. Place your press as close as you can to the shaped cookie next to it. The space of the press itself is enough.
See photos for tips on how much dough to let out while you are pressing. Basically, the fatter you make your cookies, the more they will puff in the oven, and you risk not being able to recognize the shape as well. For really pretty, well-defined spritz cookies, press out the least amount of dough that you can per cookie.
At this point, you can choose to sprinkle the cookies with colored sanding sugar if you like. It's much easier doing it before baking than doing it after, but I don't love the way it looks. (You almost always get sprinkles pooled on the outer edges of your cookie.)
Bake the cookies at 375 for about 6 minutes. If you used a very dainty shape or don't trust your oven, start with 5 minutes. The larger cookies might take 7 minutes. The cookies are done when they are set (slightly firm) on the edges and no longer shiny. They should not be brown on the edges. If you see any browning or golden-ing, take them out immediately. (My mother-in-law Kris will argue with me about this until her dying day. But I said what I said. Spritz cookies should NOT be brown!) Bake all the same shape cookies on the same pan to avoid over/under baking. It's best to bake the same color dough all on the same pan too.
Let the cookies set on the pan for 2-3 minutes. Transfer to a cooling rack and let cool completely.
If you would like to add a glaze, in a medium bowl whisk together 1 cup powdered sugar, 1 tablespoon corn syrup, 1/4 teaspoon almond extract, and start with 1 tablespoon milk. Whisk it together and decide if you want to add more milk to get a thinner consistency. See photos. You want a fairly thin glaze.
Once the cookies are cool, use a pastry brush to lightly brush each cookie with the glaze. (You can also brush with water or straight corn syrup). Dust each cookie with sanding sugar or sprinkles. Let set up on the cooling rack.
These cookies should be stored well covered on the counter. They will keep for 3-5 days.
Freezing: Spritz cookies freeze very well! We do it every year so that we don't eat them all at once. Freeze in a sealed container and then let thaw in the sealed container at room temperature. Or dip frozen ones in hot chocolate. I mean I'm just guessing this is really good, I'm definitely not the one pilfering from the freezer stash.