Pull out your 9-inch springform pan. Pour the crumbs and 1/2 cup sugar into the bottom. Toss thoroughly with a fork. Drizzle the butter over the crumbs and then use your fork to combine. You save washing a bowl with this method. Make the crust right in the pan. Spread the buttered-up crumbs with your fingers across the bottom of the pan and halfway up the sides. You don't have to be precise.
Open the softened ice cream and, by scoops, fill the springform pan. You can layer the scoops or just assort them around the pan as you choose. With a table knife, gently spread the ice cream so it evens up pretty well. Put this in your freezer to begin hardening while you make the topping.
In a sauce pan, combine 3/4 cup sugar, orange juice, and cream of tartar. Bring to a low boil and stir while the sugar melts. This should take a couple of minutes. Raise the temperature slightly so you have a quiet boil going. You're taking the temperature up to 240 degrees if you have a candy thermometer, but if you don't, watch for the point when it starts to thicken up and darken slightly. Stay near in case it's tempted to try to boil over. Thickening should take about 5 to 7 minutes. Now take it off the heat and stir in the pecans. If you've used a large enough sauce pan, they can all fit; otherwise combine the sugar sauce and pecans in a bowl. When the pecans and sugar sauce are mixed, sprinkle on the cinnamon and mix one more time.
Take your partially hardened ice cream torte out of the freezer and carefully pour on the pecan mixture. No need to really decorate with it. Just spread it around to the edges. Quickly get it back in the freezer because the warm pecans will soften up the ice cream more, and some of the melted parts will rise to the top. That's okay. It should stay in the container just fine. It's never leaked on me. Keep the torte in the freezer at least four hours to fully harden.
When you want to serve it, run a sharp knife around the inside edge of the springform pan. Loosen the latch and take the torte out. Cut into slices with the same sharp knife.