Add the onions and cook slowly until deep golden color.
Add vinegar and thyme and season with salt and pepper, cook for 2 minutes longer. Cook potatoes in a large pot of salted water until soft.
Drain well, add butter, heavy cream and horseradish, mash until smooth. Season with salt and pepper.
Place potatoes in a bowl and top with the onions.
Heat oil in a medium saute pan.
Add squash and saute until just cooked through.
Add butter and cook until melted.
Add parsley and season with salt and pepper to taste.
Pan Seared Cod:Preheat oven to 375 degrees F.
Heat oil in a large saute pan. Season cod on both sides with salt and pepper. Dredge skin-side in cilantro.
Place cod, cilantro-side down in the oil and saute until lightly golden brown. Turn the fish over and place in the oven and continue cooking for 3 to 4 minutes until just cooked through.