Ginger Lime Ponzu Sauce:
Combine ingredients and blend together using a whisk or an immersion blender. Transfer to a plastic container with a snap on lid. Sauce will hold for several days and can be scaled to desired quantity for production.
In a large mixing bowl, combine tempura batter mix with ice-cold water. Refrigerate batter until ready to use. Prepared batter will last for several hours, but it is not advised to keep overnight. If batter has been sitting for more than a few minutes, whisk to combine. If batter thickens over time, dilute with ice cubes and allow to melt before using.
Combine cut vegetables in a mixing bowl and add dry tempura mix to coat. This should be done on a per order basis; otherwise moisture from vegetables will cause the batter mix to clump.
Submerge dredged vegetables into prepared tempura batter; stir to ensure they are completely coated with batter. Pinch desired portion of vegetables, per haystack, between tongs, tap tongs gently to shake off any extra batter and slowly submerge into 350°F oil. Hold haystack together with tongs for 15 to 20 seconds or until batter is set. Release tongs and repeat process as needed. Fry hay stacks for approximately two minutes, turn over and fry another 2 minutes, or until golden brown. Fry times will vary based on oil temperature and number of haystacks in the fryer.
When haystacks are golden brown, pull from fryer with a spider and drain on paper towels.
Stack five haystacks on a plate and serve with Ginger Lime Ponzu Sauce.
Note: Vegetables for haystacks can be substituted based on cost and season.