Homemade marzipan is much tastier than store-bought, and a lot less expensive.
Sift the almond flour and confectioners sugar together into a large bowl and mix them until they are well combined. The mixture looks like a pillowy, off-white powder.
Mix the almond extract and corn syrup together, then add them to dry ingredients.
Add water very slowly, by no more than half tablespoons at a time, working the mixture until it becomes dough-like. I usually begin with a fork or spatula, then switch to using my hands. Try to use no more than 1-2 tablespoons of water total - use the minimum amount that will, with the heat of your hands mixing the ingredients, allow you to roll it into a log.
Put the log into a gallon-size freezer bag, gently roll the log a bit more to smooth it out, and refrigerate the log for at least one hour before serving or using in baked goods.
The recipe uses only 4 ingredients, 5 if you count water.
Use well-blanched almond flour that is light tan in color, not almond flour that contains the dark skins of the almonds.
I used store brand almond extract. Although I was tempted to buy the expensive stuff, it turns out that when my son, Liam, and his friends did an almond extract taste test, the store brand was actually preferred by several of my taste testers.
To serve the marzipan on its own, slice the log into pieces 1/4-1/2 inch thick.