01 - In a saucepan, combine the peeled and sliced parsnips, diced potato, garlic cloves, and whole milk. Bring to a gentle simmer over medium heat and cook uncovered until the vegetables are fork-tender, approximately 15 to 18 minutes.
02 - Drain the vegetables, reserving a small amount of the cooking milk. Transfer the parsnips, potato, and garlic to a blender or food processor. Add the unsalted butter, season with salt and white pepper, and purée until silky smooth. Use the reserved milk to adjust consistency as needed. Keep warm.
03 - In a small saucepan, combine the dry white wine, freshly squeezed orange juice, lemon juice, and finely chopped shallot. Bring to a simmer and reduce the mixture until only about 3 tablespoons remain, concentrating the flavors.
04 - Reduce the heat to low and slowly whisk in the cold butter cubes, one at a time, until the sauce is velvety and emulsified. Strain through a fine-mesh sieve to remove the shallot pieces. Season with salt, pepper, and lemon zest. Hold warm but do not allow to boil.
05 - Pat the halibut fillets thoroughly dry with paper towels and season both sides generously with salt and freshly ground black pepper. Heat the olive oil in a large non-stick skillet over medium-high heat until the oil just begins to shimmer.
06 - Carefully place the seasoned fillets in the hot skillet and sear for 3 to 4 minutes on the first side until a deep golden-brown crust forms. Gently flip and continue cooking for another 3 to 4 minutes until the fish is just cooked through and flakes easily.
07 - Spoon a generous portion of the warm parsnip purée onto the center of each plate. Lay a seared halibut fillet over the purée, drizzle generously with the citrus butter sauce, and finish with a sprinkling of freshly chopped chives. Serve immediately.