1) Preheat oven to 350 degrees F. Lightly butter an 8×8 baking dish.
2) Stir together pistachios, chocolate, 1/4 cup sugar, and cinnamon. Set aside. Also whisk together flour, baking powder, baking soda, and salt in a medium bowl.
3) In a large mixing bowl, cream together butter and remaining sugar. Then mix in vanilla and eggs, one at a time.
4) Mix in 1/3 of the dry ingredients, followed by 1/2 of the yogurt, another 1/3 of the dry stuff, the rest of the yogurt, and the last of the dry ingredients. Mix until the batter is just combined.
5) Spoon half of the batter in to the buttered baking dish and top with half of the chocolate and pistachio mixture. Top with last of the batter and finish the cake by topping it with the rest of the pistachio mixture.
6) Bake cake at 350 degrees F. for 40-45 minutes. Let cool for 10 minutes once it has baked and then slice and serve!