Preheat oven to 350 degrees F. Put the almonds and brown sugar into a food processor. Chop to a fine meal. Transfer to a bowl. Put flour, baking powder, salt, and cinnamon into processor. Process for several seconds. Add butter and process again to make a fine meal. Mix into the ground nuts. Beat eggs just to liquefy; stir in the vanilla. Mix liquid into dry ingredients by hand until dough packs together.
Divide dough in half. Roll each half in confectioners’ sugar into a 2-inch-thick log. Lift each log onto greased cookie sheets and flatten slightly. Bake for 35 minutes. Turn oven down to 300 degrees F. Cool logs for 10 minutes on sheets, then slide them onto a cutting board. Slice logs on the diagonal, about ½ inch thick. Place the slices back onto the sheets, standing on their original bottoms. Bake for 30 minutes longer. Cool on a rack.