Make the dipping sauce: Combine all ingredients in a bowl. Set aside to allow the flavors to develop.
the shrimp by cutting down the back, being careful not to cut all the way through. Open the shrimp like a book and rinse well with cold water.
Make the Tempura batter
: Put 1 cup of rice flour
in a bowl and pour in the seltzer. Stir with a whisk
to get out all the lumps. Add the egg
yolk and blend
it in well. The batter should be the consistency of heavy cream
. Flavor with sesame oil, if using.
Heat about 2 inches of vegetable oil to 375 degrees F in a wok
or deep fryer. Dry the shrimp well. Dust
in flour to soak up any remaining moisture, shake off excess. Dip the shrimp into the batter one by one. Drop 4 or 5 pieces at a time in the hot oil. Do not overcrowd the pan. Fry
until golden brown, turning once, about 3 minutes. To keep the oil clean between batches, skim
off the small bits of batter that float
in the oil. Remove the fried shrimp from the oil and drain
on paper towels; season them with salt. Serve with the dipping sauce.