Line a baking sheet with parchment paper. Line a bamboo steamer with parchment paper and place it in a pot filled with 2 inches of water. Set aside.
To make the filling, in a large bowl, combine the beef, shrimp, Cheddar, shallot, scallion, vinegar, sesame oil, soy sauce, cornstarch, garlic powder, ginger and pepper and mix with your hands until evenly combined. Set aside.
In a small bowl, beat the egg with 2 tablespoons of water until combined. Set aside.
To assemble the shumai, gently roll 2 tablespoons of filling into a ball, just as you would a meatball. Transfer the ball to the prepared baking sheet. Repeat with the remaining filling, leaving about 1 inch between balls.
Use your finger to wet the middle of a wrapper with some beaten egg. Place the wrapper over a meatball and gently press into the meatball; invert the wrapper to partially enclose the filling. Pinch the wrapper gently to secure it around the filling. Transfer the shumai to a piece of parchment paper and repeat with remaining wrappers and meatballs.
Bring the water in the pot fitted with the bamboo steamer to a simmer. Place the shumai in the basket, leaving about 1/2 inch between each (work in batches if necessary). Steam until cooked through, 8 to 10 minutes.
For the dipping sauce: Whisk together the sriracha and soy sauce in a small bowl. Serve with the steamed shumai.