Editor’s note: The theme of Gohan Lab is to help people make simple, tasty “gohan” (meals).

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The appeal of cooking prawns in their shells lies in the rich flavor that wafts up, conjuring aromas of a barbecue on the beach. This week’s recipe introduces a Chinese-style delicacy where the umami blends into the ketchup-based sauce.

Unshelled prawns that are little on the large side, say 12 to 13 centimeters in length, work best. For example, king prawns known as “banamei” have softer shells and can be eaten whole.

Do not overcook, or the prawns will lose their springy texture. Preparation, as is so often the case, decides the outcome.

The actual cooking time is about five to six minutes.

But it is important to prepare the ingredients for the sauce beforehand. They must be mixed and the vegetables prepared, with the serving plate lined up close by.

There is a reason for adjusting the heat level midway through the cooking process. Placing cold ingredients into a frying pan reduces the temperature, so the heat needs to be raised. But as soon as the ingredients come to the boil, the heat should be lowered to maintain an optimum temperature.

In response to the question, “Which single ingredient would you add to make the dish more filling?” Katsuhiko Yoshida, who oversaw the cooking aspect of the dish, offered the unexpected choice of sweet potato. Its sweetness and unsoggy texture proved just right.

THAW QUICKLY

When cooking frozen prawns, the key to retaining freshness is to thaw only the amount you will be using and cook right away. The texture and color when heated will be better if the thawing time is short and the temperature is kept low.

Yoko Ishii of Tsukurin, a middle trader specializing in shrimp and prawns who operates in Tokyo's Toyosu Market, suggests thawing them under running water in winter when the tap water is cold. Place the prawns in a plastic bag, squeeze out the air and place under running water. “In other seasons, immerse the bag in iced water.” Ishii does not recommend thawing at room temperature or in the fridge.

You will know if frozen prawns have started to get freezer burn if the shell looks whitish and raised from the meat. When storing prawns in home-use freezers, it is better to consume them within a month of purchase.

BASIC COOKING METHOD

(Supervised by Katsuhiko Yoshida in the cooking aspect)

* Ingredients and cooking utensils (Serves two to three)

6 unshelled headless prawns (180 grams), katakuriko starch, 80 grams sweet potato

For ketchup-based sauce: 1 tsp grated garlic, 1 tsp grated ginger, 2 Tbsp ketchup, 2 Tbsp sake, 2 tsp sugar, 150 ml water, 1/3 green onion (naganegi), 4 thin green onion (konegi)

1. Remove legs and tip of tails with kitchen scissors. Cut open along center of back from head to beginning of tail (PHOTO A). Devein. Rinse briefly and pat dry surface. To season beforehand, apply salt, pepper, sake, katakuriko starch (all not listed above) in this order on the part that is cut open.

2. Chop green onion, slice konegi. Cut sweet potato into 1.5-cm square dices with skin. Mix water, grated garlic and ginger, ketchup, sake and sugar to make sauce. Mix 1 tsp katakuriko starch with 2 tsp water in separate bowl.

3. Place frying pan with 1 Tbsp oil and sweet potato on medium heat. Brown while mixing. Cook until bamboo skewer sticks in smoothly (PHOTO B). Remove from pan.

4. Add 1 Tbsp oil and shrimps in frying pan and place over medium heat. When color of shell turns red, turn sides. Aroma of prawns will rise. Add sauce and turn up to high heat. When sauce comes to a boil, lower to medium heat, taste and add about 1/2 tsp salt if preferred. Add sweet potato and turn sides of prawns. Add green onion and konegi (PHOTO C) and raise to high heat. When it comes to a boil, turn off heat. Add water-katakuriko mixture and mix. Turn on heat and bring to a boil while stirring to thicken sauce.

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Katsuhiko Yoshida is the owner chef of Jeeten, a restaurant in Tokyo’s Yoyogi Uehara offering Chinese home cooking.

ARRANGED VERSION

<Prawns in chili sauce>

Try making a chili-sauce version by adding a piquant flavor. When mixing the ketchup-based sauce, add 1/2 tsp doubanjiang paste and 1 tsp vinegar. The latter takes the edge off the spiciness. Sweet potato may be added.

COOKERY SCIENCE

Prawns curl up when heated due to the difference in the muscles on the dorsal and ventral sides. The “fast-twitch muscle” that gives instantaneous force is found on the dorsal side. The “slow-twitch muscle” with staying power thinly covers the underside where the legs move constantly to swim.

Since the slow muscle contracts significantly more than when the fast muscle when heated, incisions are made in the ventral side so the prawns turn out straight when deep-fried for tempura. (Cookery science aspect supervised by Shugo Watabe, Project Professor, School of Marine Biosciences, Kitasato University)

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This column, translated from The Asahi Shimbun’s Gohan Lab column, will next appear on Jan. 29.