Prep the pan: Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners and spritz the liners with nonstick spray.
Whisk the dry ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
Beat the wet ingredients: In a large bowl, beat the oil and ¾ cup of sugar with an electric mixer on low, then on medium-high for 2 minutes. Add the eggs one at a time, mixing after each. Mix in the vanilla, orange zest (if using), and sour cream until smooth.
Add the dry ingredients: With the mixer on low, gradually add the flour mixture. Mix just until the batter is very thick and smooth, with no dry flour left. Don't overmix.
Add the cranberries: In a small bowl, toss the cranberries with the remaining 2 tablespoons of sugar. Gently fold them into the batter with a spatula.
Fill the cups: Divide the batter evenly among the muffin cups, filling them nice and full. Sprinkle the tops with about ½ teaspoon of coarse sugar each, if using.
Bake: Bake for 18 to 22 minutes, until the tops are lightly golden and a toothpick in the center comes out clean.
Cool: Move the muffins to a wire rack and let them cool completely.