Preheat your oven to 400℉. Line your muffin tin with muffin cups.
Sift together the flour, baking powder, and baking soda; set aside.
1⅔ Cups Flour, 1¼ Tsp Baking Powder, ½ Tsp Baking Soda
In your mixer, beat together the eggs and sugar until light and fluffy, about 3-4 minutes.
⅔ Cup Sugar, 3 Eggs
Add the milk, vanilla extract, and orange zest, to the egg and sugar mixture. Mix this well for another minute, and keep the mixer going on low.
⅔ Cup Milk, 2 Tsp Vanilla Extract, 2 Tsp Orange Zest
Slowly add the melted butter to the mixer until it's fully combined.
½ Cup Butter
Using your rubber spatula, fold in the flour mixture about a third at a time. Gt it incorporated but avoid over-mixing it, which will make the mantecadas dense.
Let your batter rest for about 15 minutes, allowing the baking powder and soda to activate.
Fill your muffin cups about ¾ of the way full with batter. Since they will rise while baking, you don't want to over-fill them. Optionally, you can top each cup with a bit of finishing sugar.
Turn the oven heat down to 350℉ and put the tin in the oven. Bake for 15 minutes, or until a toothpick inserted into the middle comes out clean.
Let the muffins cool for a bit before removing onto a wire rack to cool completely, then enjoy!