In a large pot of salted boiling water, cook the potatoes until tender. About 20 minutes.

In the meantime, while the potatoes are boiling, combine flour and cayenne in a medium bowl. Add leeks and toss to coat.

In a medium saucepan over medium heat, heat 2-inches of oil until a thermometer registers 350 F.

Working in batches, add leek rings and cook, turning until crisp and light golden around edges, about 1 minute.

With a slotted spoon, transfer leeks to paper towels to drain.

Season with salt. Set aside.

Once potatoes are tender, drain well and return to the pot that they cooked in.

Add 1/2 cup butter, milk, salt and pepper. Using a hand mixer, mix until smooth.

Add mustard and fold in with a spoon until combined. Keep warm.

Next, in a nonstick skillet over medium-high heat, melt 2 Tbsp. butter.

Salt and pepper the salmon and place in the pan skin side up.

Cook, without turning, for 5 – 6 minutes, until the flesh turns deep brown.

Flip and cook for another 2 – 3 minutes.

When salmon is ready, plate the potatoes and top with the salmon.

Sprinkle fried leeks over the salmon and potatoes and serve.