Grease 8 x 8-inch pan or line with parchment paper. Heat a large saucepan over high heat until a drop of water sizzles in the bottom. Add the amaranth a few teaspoons at a time (if you try to pop too much at once, it won’t pop and will burn). Within a few seconds, it should begin to pop. Continue stirring until almost all of the grains are popped. Pour into a bowl and pop your next batch until you have 1 1/2 cups of popped amaranth. Pour maple syrup into a saucepan over medium-high heat and bring to a soft boil, stirring constantly. Boil for 12 minutes, or until it measures 244 F on a candy thermometer. Remove from heat and add the cinnamon and pistachios. Mix well, then add the popped amaranth. Pour into the greased pan and press it in evenly. Allow to cool slightly before cutting, but don’t let them cool all the way or they will be more difficult to cut. Store in an air-tight container.