Karashi Renkon is a popular regional dish on the island of Kyushu in Japan. A mixture of miso and Japanese karashi hot mustard is stuffed in lotus root, coated in turmeric flour batter, and deep-fried until a crispy crust forms.
Peel the lotus root and scrape the sides lengthwise with a fork. Creating a rough surface helps the batter stick to the lotus root.
Trim both ends. If the lotus root is longer than 4" (10 cm) in length, cut it in half. Place the lotus root in a saucepan and add just enough water to cover. Add 1 tsp rice vinegar to prevent the lotus root from changing color.
Bring the water to a boil and cook for 6 minutes. Transfer to a sieve and let it stand upright to dry until the holes are completely dry (excess moisture will dilute the fillings).
In a bowl, combine 2 tsp karashi mustard and 1 Tbsp warm water and mix well.
In a medium bowl, combine 5 Tbsp panko, 1 Tbsp mirin, 1 Tbsp sugar, and 5 Tbsp white miso and mix well.
Add in the karashi mustard and mix all together.
Pile the mustard miso mixture into a small mound on a plate. Press the lotus root into the mixture repeatedly until it fills up the holes and overflow from the top.
Wipe off the excess mustard and let it stand upright on a clean plate. Cover with plastic wrap and keep in the refrigerator overnight for the best result (or minimum 5 hours).
Next day, remove the excess mustard miso mixture from the top and bottom and wipe off the excess moisture with paper towel.
In a large bowl, beat 1 egg and sift 1 cup flour, 1 tbsp turmeric and ¼ tsp kosher salt into the bowl.
Mix all together and gradually add ½ cup water.
Stir until blended. The batter will be sticky and thick so it coats the lotus root well.
Add 3 cups oil in a small pot and bring the oil to 350ºF (180ºC) over medium heat. The oil should cover the lotus root when deep frying. Therefore, a smaller pot works better so you can use less oil.
Insert 2 bamboo skewers into the side of the lotus root. Dredge the lotus root in the batter.
Using a spoon, make sure the lotus root is completely covered with the batter. Ideally, you want to smooth out the surface. (I know, it can be challenging, as the batter tends to fall off when you touch it. Let’s do your best.).
When the oil reaches 350ºF (180ºC) (or drop a small amount of the batter in the oil and if it floats back to the surface in a few seconds, it’s ready.), submerge the lotus root, holding the bamboo sticks. Deep fry for 5 minutes. Make sure the lotus root is NOT TOUCHING the bottom of the pot; otherwise, the batter will stick to the bottom. Deep fry until crisp and golden brown. Drain excess oil on the wire rack until it’s cool enough to handle.
Slice the Karashi Renkon into ⅓ inch (8 mm) thick rounds. Serve immediately.
You can keep the leftovers in an airtight container and store in the refrigerator for up to 2 days or in the freezer for 3 weeks.