Tempura Shrimp and Vegetables

Ingredients
For dipping sauce
1/4 cup dashi
1/2 cup light soy sauce
2 teaspoons fresh ginger, finely grated (from about 2 cm piece)
1/2 cup daikon radish, finely grated (from about 12 cm piece)
1/4 cup mirin (Japanese sweet rice wine)
For tempura
10 green beans, trimmed
12 large shrimp, peeled, deveined, tail shells left intact
Salt and pepper
About 6 cups vegetable or peanut oil for frying
2 cups all-purpose flour
1 1/2 tablespoons baking powder
2 tablespoons Asian sesame oil
10 fresh shiitake mushrooms (about 350 g), stemmed
1 large white onion, peeled and cut into 1 cm thick rings
60 g piece fresh lotus root (about 4 cm long), peeled, and cut into 1 cm thick slices
10 fresh shiso leaves

Preparation
Make dipping sauce

In small saucepan over moderate heat, stir together all ingredients. Bring to simmer, then remove from heat and keep warm. (DO AHEAD: Sauce can be made ahead, refrigerated in covered container up to 2 days, and rewarmed over moderate heat before serving.)
Make tempura

Bring medium pot water to boil over high heat. Have large bowl ice water ready. Add green beans to boiling water and blanch just until crisp-tender, about 30 seconds. Using slotted spoon, immediately transfer to ice water to stop cooking, then drain well and dry on paper towels.
Make several shallow cuts across inside curve of each shrimp and gently press shrimp flat on cutting board (to help prevent curling during cooking). Sprinkle shrimp with salt and pepper.
In large saucepan over moderate heat, heat 10 cm of oil until thermometer registers 170°C.
In large mixing bowl, whisk together flour, baking powder, and sesame oil. Gradually and gently whisk in 2 1/2 cups ice water, mixing just until dry ingredients are moistened. (Batter will be very lumpy.)
Working in batches, using tongs or chopsticks dip shrimp and vegetables into batter and fry, turning occasionally, until golden, about 1 1/2 minutes for green beans, 2 minutes for shrimp and other vegetables. Transfer to paper towels to drain. Return oil to 170°C between batches and, using spider or slotted spoon, remove any residual bits of batter from oil before adding next batch.
To fry shiso leaves, gently lay each leaf on top of batter to coat 1 side, then drop, batter-side-down, into oil and fry without turning until underside is golden, about 1 minute. Transfer to paper towels to drain.
Serve tempura immediately with dipping sauce.