Soften the butter to room temperature.
Fine mince the shallot.
If using fresh or roasted garlic, mince the garlic.
Juice the mandarin oranges and lemon juice.
In a bowl, break down the butter until it is smooth.
Combine all ingredients and mix well to combine.
The lemon and orange juice may not fully incorporate into the butter. If it doesn't refrigerate for 10-15 minutes to firm up the butter. Don't let the butter become too hard.
After the butter has firmed up in the refrigerator, try to fold the butter and citrus juice to incorporate the juice. If it still does not incorporate, no worries.
Lay out about 12" of plastic wrap on the counter. Place the mixed compound butter onto the center of the plastic wrap.
Form the butter into a cylinder.
Fold the plastic wrap closest to you over the compound butter.
Roll the plastic wrap and butter so it covers the bitter tightly.
Hold the ends of the plastic wrap at both ends of the rolled butter.
While holding the ends, roll the plastic wrapped butter back toward you.
The cylinder of butter should tighten as you roll.
Refrigerate the compound butter for 1 hr to overnight to harden.
When ready to serve, remove the compound butter from the refrigerator and slightly soften. You can cut rounds of butter or crumble. In this recipe it will not matter if it crumbles because the butter will be melted over the fish.