Preheat oven to 350 degrees F (180 degrees C).
Put Fingerling Potato (8 ounce) and Salt (1 teaspoon) in a medium saucepan and fill with enough water to cover potatoes. Place the pot over high heat and bring to a boil. Once the water is boiling, cook for 14 minutes, or until potatoes are fork tender.
Drain potatoes into a colander, let cool slightly, and then cut the potatoes in half lengthwise.
Meanwhile, cut the Leek (6 ounce) into half inch diced pieces, and set aside. Remove the stems from the Fresh Thyme (0.25 ounce) and discard stems. Finely chop the thyme leaves and set aside.
Pat dry the Mahi-Mahi Fillet (2) with paper towels and rub the Blackening Seasoning (1 tablespoon) onto one side of the fillet, making sure the fillets are well coated. Set aside.
Heat the Butter (4 tablespoon) in a medium saute pan over medium heat. Once the butter has melted, add the leeks and saute for 3-4 minutes until fragrant and translucent.
Add fingerling potatoes and thyme to the pan and season with Salt (1/4 teaspoon) and Ground Black Pepper (1/4 teaspoon). Cook for 3-4 minutes or until potatoes are heated through. Remove from heat and set aside.
Heat a medium oven proof saute pan over medium high heat and add Olive Oil (1 tablespoon). When oil is hot, add the mahi mahi fillets spice side down, and sear for three minutes.
Place the saute pan in the oven and finish cooking for 4-5 minutes.
In the center of two plates, place the potatoes and leeks. Top with blackened mahi mahi.