Peel potatoes, cut into chunks and put them in a saucepan of salted water. Bring to a boil and cook for 10-15 minutes or until tender. Drain and leave them in the colander to completely steam dry.
Blend cooked beetroot with mascarpone cheese and season with salt and pepper. Set to one side.
Flake your smoked mackerel fillets with a fork into small pieces. Finely dice your herbs, zest the lemon.
Prepare your panko station. Take 3 bowls or Tupperware containers and place the flour into one, the egg into another, and the panko breadcrumbs into the third.
Mash your potato in a large mixing bowl and then mix with the flaked smoked mackerel fillets, lemon zest and herbs.
Take a large teaspoon of the smoked mackerel and potato mixture. and shape it into a ball with your hands. Press it together to compress it, then roll it to form a sphere.
Panko the smoked mackerel croquettes by dipping them first into the flour, making sure each side is coated. Then dip them into the egg, and then into the panko breadcrumbs.
Heat a small frying pan with oil. Using a small frying pan allows you to get a deeper layer of oil for optimum shallow frying, aim for a depth of half a centimeter.
When the oil is shimmering, fry the smoked mackerel croquettes in small batches turning occasionally to get each side golden and crispy.
Place the smoked fish croquettes onto kitchen paper to soak up any excess oil after cooking, and then put them on your serving plate.
Using a teaspoon, place a small amount of beetroot puree on top of each smoked mackerel croquette. Garnish with a small sprig of chive, and serve.