Preheat oven to 400 degrees. Line muffin tin with paper liners. Set aside.In a medium mixing bowl, whisk together flour, baking powder, soda and salt. And zest and stir.In a large mixing bowl of a stand mixer, cream butter and sugar until fluffy.Add eggs, one at a time, mixing well after each addition.Add vanilla and mix well.With mixer on low speed add dry ingredients ½ cup at a time, alternating with yogurt.Add chocolate and stir it in with a wooden spoon.Scoop the batter out to lined muffin tin, filling all the way to the top. You can place few chocolate chips on top of each muffin.Bake for 5 minutes in 400 degree oven, Reduce the temperature to 375 degrees and bake 15 more minutes, or until browned on top and toothpick inserted in the center of each muffin comes out clean.Cool in pan for 2 minutes, then transfer to a wire rack to cool completely.You can wrap baked muffins tightly and freeze for up to 1 month. Simply defrost on the counter and pop in the microwave for 7 to 10 seconds to warm up and make chocolate melty.