Set up an assembly line for the nut crust. Mix panko crumbs and macadamia nuts on a flat plate. Whisk the egg in a shallow bowl. Place the flour on another plate.
Now dredge the grouper in the flour, shaking off excess, then dip into beaten egg, and lastly, dredge in the crumb mixture, patting so they adhere.
In an oven-proof skillet, over medium heat, heat olive oil until hot. Place fillets in the pan and brown on one side for 3-4 minutes. Turn fillets over and place entire skillet in the oven and bake for 10-15 minutes, depending on thickness. Grouper is fully cooked when it flakes easily with fork. NOTE: Only use skillets that are oven safe, usually all stainless steel.
While grouper is baking, make sauce.
Combine all ingredients, except butter, in a saucepan over medium-high heat. Cook, stirring occasionally, until reduced by half, about 10-15 minutes. Remove from the heat and stir in butter.
Plate the baked grouper over rice or spinach, then drizzle a small amount of sauce over the top. Serve the extra sauce on the side.
Notes
STORE/FREEZE/REHEATSTORE the grouper in an airtight container in the fridge for up to 3 days. Keep the sauce in a separate container.FREEZE the cooled fillets in plastic wrap then place in a freezer-safe bag or container. They’ll keep for about 2 months. Freeze the sauce separately in a small container.REHEAT the fish in a 350°F oven for 8-10 minutes or until heated through. Reheat the sauce gently in a saucepan over low heat, stirring frequently.