1) Preheat the oven to 375°F. Lightly grease (or line with parchment) two baking sheets.
2) Beat together the butter and sugar until smooth.
3) Add the egg, beating until smooth.
4) Beat in the vanilla, salt, and baking powder.
5) Add the flour, mixing until totally incorporated.
6) To make the coating: Shake together the sugar and cinnamon in a medium-sized zip-top plastic bag.
7) Drop 1" balls of dough into the bag; a teaspoon cookie scoop works well here. Roll/toss the cookies in the cinnamon-sugar until they're completely coated.
8) Space the cookies at least 1 1/2" apart on the prepared baking sheets. Use a flat-bottom glass to flatten them to about 3/8" thick; they'll be about 1 1/2" in diameter.
9) Bake the cookies for 8 minutes (for soft cookies) to 10 minutes (for crunchier cookies). Remove them from the oven, and cool them on the pan until they're firm enough to transfer to a rack to cool completely.
Yield: 3 1/2 dozen cookies.