Preheat the oven to 180°C.
Line a cupcake tray with cupcake liners or lightly grease the cups.
In a large mixing bowl, combine the melted butter and powdered sugar.
Mix until the mixture becomes lighter in color and smooth in texture.
Add the eggs one at a time, mixing well after each addition.
Add the curd, honey, and vanilla extract.
Mix until fully combined.
In a separate bowl, sift together the refined flour, baking powder, and salt.
Add the mandarin zest to the dry ingredients and mix gently.
Gradually add the dry mixture to the wet mixture, alternating with the room-temperature milk.
Mix gently after each addition until just combined.
Add the orange juice.
Mix once more until the batter is smooth and evenly combined. Do not overmix.
Divide the batter evenly among the prepared cupcake liners, filling each about two-thirds full.
Bake for 18 to 20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean.
Remove the cupcakes from the oven.
Allow them to cool in the tray for a few minutes.
Transfer the cupcakes to a wire rack and allow them to cool completely before frosting.
To prepare the buttercream frosting, place the room-temperature butter in a mixing bowl.
Beat on high speed for 4 to 5 minutes, or until the butter becomes light, creamy, and pale.
Add the vanilla extract and mix until incorporated.
Gradually add the powdered sugar, a little at a time.
Continue beating until the frosting is smooth, creamy, and firm enough to hold its shape.
Once the cupcakes are completely cool, pipe or spread the buttercream frosting over the tops.
Serve as desired.