Add the thinly sliced beef into the Instant Pot along with beef broth, garlic powder, salt, and pepper. Stir to combine and coat the beef. Secure the lid, set the valve to sealing, and cook on High Pressure for 10 minutes.

Allow for a natural pressure release for 10 minutes, then switch the valve to venting for a quick release. Open the lid to reveal tender beef.

In a medium saucepan, melt the unsalted butter over medium heat. Whisk in the all-purpose flour, stirring constantly for 1-2 minutes until it turns a light golden color.

Slowly pour in the milk while continuously whisking. Cook until thickened, about 5 minutes. Stir in hot sauce and salt, adjusting spice level, then add sharp cheddar cheese in batches until melted.

Toast the onion hamburger buns in a skillet or oven to achieve a golden exterior, preventing sogginess.

Assemble the sandwiches by placing a generous portion of beef on each toasted bun and top with the spicy cheese sauce. Add optional garnishes as desired.

Serve immediately, pairing with crispy oven-baked fries or a fresh salad.