First you need to toast the flour in the oven. To do so, spread it out on a baking sheet, and bake under the broiler (250ºC/480ºF) until the top layer browns. Remove the flour from the oven, mix it up spread it out on the baking sheet again and bake until golden. Repeat the process 4-5 times until all of the flour is toasted and golden brown. Keep your eye on it so it doesn't burn!
Toast the ground almonds in some of the lard in a pan on the stove. Once they are a golden brown, remove them from the stove and let them cool.
Once your ingredients have cooled, mix all of the ingredients together making sure to incorporate all of the lard. The "dough" should come together when you press on it, but should easily fall apart. You may need to add in a little more lard to achieve the right texture. (Don't add in too much or you will end up with hard cookies rather than crumbly soft ones when you bake them.)
Put the "dough" into the fridge for 15-20 minutes.
Preheat the oven to 180ºC/350ºF.
Working with small sections, roll out the dough with a rolling pin to around a half on an inch thick (or slightly thicker).
Cut the dough with cookie cutters. These would be perfect. Mantecados are typically round, and polvorones are typically oval, but you are free to make them as you like. These cookies are delicate, though, so I don't suggest any complicated shapes.
If you want to decorate them with sesame seeds, lightly press some into the top of the cookies now.
Bake in the oven for 12-15 minutes or until the edges turn a golden brown.
You may leave them as is or sprinkle powdered sugar over top.
Serving size based on a large cookie almost an inch thick and 2 inches in diameter.