Mexican Shortbread Cookies

Preheat the oven to 350 degrees.
Spread the almonds and the flour on separate baking sheets.
Place both in the oven and bake until the almonds are toasted and the flour is a deep creamy color, about 12 to 15 minutes, stirring the flour and the almonds once.
Set aside to cool completely.
Place the almonds and the sugar in a food processor and process until the nuts are ground.
Sift the flour with the salt and baking powder into a large mixing bowl.
Stir in the almond mixture.
Add the butter and shortening, working it in with your fingers until you have a crumbly dough.
Press the dough together, flatten and wrap in plastic wrap.
Refrigerate for 2 hours.
Butter a cookie sheet well.
Unwrap the dough and place it on top of the plastic wrap; cover it with another sheet of plastic wrap.
Using a rolling pin, roll the dough out between the sheets of plastic with quick, short movements until it is about 1/4 inch thick; it will be crumbly around the edges.
Using a cookie cutter 2 inches in diameter, cut out as many cookies as you can.
Transfer them to the cookie sheet with a spatula, being very careful or they will break apart.
Gather up the remaining dough and roll out and cut out more cookies.
Repeat until all of the dough has been used.
Bake the cookies on the top rack of the oven until they are pale golden in color, about 10 to 15 minutes.
Sift the confectioners' sugar over them and set them aside to cool before removing them from the cookie sheet.
Store the cookies in an airtight container.