In a bench top mixer fitted with a paddle attachment, beat the butter until smooth, about two minutes.
Add remaining ingredients and mix until thoroughly combined, another two minutes.
Lay out two 18” X 24” sheets of film wrap on a work table. Divide the butter between the two sheets and roll into 6” x 1” cylinders. Twist the ends of the plastic tightly and place in cooler for at least two hours to chill. (Makes about 1 Lb.)
Fold the parchment paper in half long end to long end. Using scissors cut paper into a half heart shape, minimizing the amount of trim.
Open the paper in front of you. Working on one half, shingle the potatoes and yellow squash on the paper on either side of center leaving a 1”border of paper clear.
Place the fillet of fish skin side up on the potatoes and squash. Top with peppers, celery, shitake mushrooms, scallions, carrots, lemon slices and herbs.
Unwrap a butter cylinder and cut two ½” coins. Place two coins on top the vegetables. Seal the parchment.
Place the parchment package on a baking sheet and bake at 400F for 10-15 minutes or until an internal temperature reaches 155F.
Transfer hot parchment packages from baking sheet to serving platter. Immediately present to customer at the table. Using a pair of presentation quality scissors or a long sharp serrated knife, open the top center of the parchment spreading open to release the steam and reveal the fish to the customer.
Take the platter with opened parchment package back to a service area and remove fish and vegetables to a serving plate and serve with accumulated cooking juices.