In a small bowl, mix butter and cinnamon together. Set aside. In a separate small bowl, mix powdered sugar with half & half until smooth. You may have to stir in a little more half & half to get it to drizzling consistency. Set aside.
Place oil and popcorn kernels into a large pot. Cover with tight fitting lid or foil. Place pot over high heat. Shake pot back and forth over hot burner to heat kernels evenly. Continue shaking the pot until the popcorn starts to pop. After a minute or two, the popping will slow right down and you'll have a pot full of popcorn. Dump the hot popcorn onto a baking sheet and drizzle with cinnamon butter immediately. Stir to coat. Drizzle the icing over the top and toss to coat as well. Serve warm, or let it cool so the icing can harden up a bit.
It's important to keep the pot moving the entire time its over the heat--this ensures the kernels don't ever burn.