Preheat oven to 350°F (175°C). Line a muffin tin with tall tulip-style cups.

Drain mandarins for 10-15 minutes. Reserve 2 tablespoons of the syrup. Pat the fruit dry with a paper towel and cut any large segments in half.

Whisk together the flour, baking powder, salt, cinnamon, and zest. Remove 1 tablespoon of this mixture for coating the craisins and nuts later.

In a large bowl, whisk the melted butter and sugar until thick. Add the eggs one at a time, mixing well after each. Add the milk, reserved mandarin syrup, and vanilla.

Add the dry ingredients to the wet ingredients. Stir gently until just combined—don't overmix or muffins will be tough. The batter should be thick—add 1-2 tablespoons extra flour if it seems loose.

Toss the craisins and walnuts with the reserved tablespoon of flour (this prevents sinking). Fold them into the batter. Gently fold in the mandarin pieces last.

Fill tulip cups just under two-thirds full. Top each with a mandarin piece if desired. Sprinkle turbinado sugar and chopped nuts on top.

Bake for 22-26 minutes until golden. A toothpick inserted in the center should come out with moist crumbs. Internal temperature should read 195-200°F.

Cool in the pan for 10 minutes, then transfer to a wire rack.