For the Chawan Mushi: In a bowl, whisk together the vegetarian dashi and beaten egg. Gently stir in the soy sauce and mirin, and season with salt and pepper. For the smoothest texture, strain the mixture through a fine-mesh sieve.
Divide the custard mixture among 4 small, heatproof ramekins.
Cover each tightly with plastic wrap or foil.
Place the ramekins in a steamer or a large pot with about an inch of simmering water.
Cover the pot and steam for 15-18 minutes, or until the custard is just set but still has a slight wobble in the center.
Carefully remove the ramekins from the steamer.
Let them cool slightly, then refrigerate for at least 30 minutes to chill completely.
For the Corn Salad: While the custard chills, combine the blanched corn kernels, shiso, and oil in a small bowl.
Season to taste with salt and pepper and set aside.
For the Vegetarian Crab Salad: In another bowl, use a fork to gently shred the drained hearts of palm.
Mix in the vegan mayonnaise, lemon juice, and lemon zest.
Season with salt and pepper, and adjust to your taste.
To Serve: Spoon the corn salad over the top of each chilled chawan mushi.
Add a dollop of the hearts of palm salad, garnish with julienned scallions, and serve immediately.