Trim off the root end of the fennel bulb. Remove any damaged outer layers, but keep the stalks if they are fresh.

Cut the fennel bulb crosswise, against the grain, into thick batons. Cut the stalks slightly smaller, as they can be tougher than the bulb.

Give the cut fennel a quick rinse and drain well.

Peel the kohlrabi and cut it into thinner batons, keeping enough thickness for a crisp texture after fermentation

Slice the green onion diagonally and set it aside.

In a large bowl, dissolve 1 tbsp coarse sea salt, about 12g, in ½ cup water.

Add the fennel and kohlrabi and toss thoroughly so the salted water coats the vegetables evenly.

Leave for 30 minutes, tossing once halfway through.

Drain without rinsing and leave the vegetables in a colander for at least 5 minutes to remove excess water.

In a small saucepan, whisk ½ tbsp flour into ½ cup water.

For a gluten-free version, use ¾ tbsp glutinous rice powder instead.

Cook over medium heat, stirring continuously, until the mixture is smooth and lightly thickened.

Remove from the heat and let it cool completely.

Add the cooled flour slurry, apple, onion in a blender, and blend until smooth. Then, add crushed garlic, ginger and pulse until garlic and ginger are finely minced. Transfer the mixture to a large mixing bowl.

Add the gochugaru and fish sauce, stir until the paste is evenly combined and deep red.

Add the drained fennel and kohlrabi and the sliced green onion into the kimchi paste.

Gently lift and toss the vegetables until every piece is evenly coated.

Do not massage, squeeze, or crush the vegetables. The fennel should stay intact, and the kohlrabi should keep its crisp shape.

Dissolve ¼ tsp coarse sea salt in ¼ cup water.

Pour the salted water into the mixing bowl and swirl it around to collect the remaining kimchi paste.

Pour it over the kimchi and toss gently once more.

Transfer the kimchi to a clean container, pressing it down lightly to remove large air pockets without crushing the vegetables.

Leave at least 20% headspace for expansion during fermentation.

Ferment at room temperature, around 20°C, for 1 day. Look for small bubbles, a slight rise in the liquid, and a gently tangy aroma rather than relying only on the time. At lower room temperature, longer time is needed (around 2 days), and at higher temperature, only a half a day is enough.

Once fermentation has started, transfer the kimchi to the refrigerator.

You can begin tasting it after a few days, but the flavor becomes more rounded after about 5–7 days in the refrigerator, as fermentation goes on.

The kimchi will last as long as it's submerged in its brine. Try at different stages of fermentation.