Cook rice with water and butter together in a rice cooker (if serving with stir fry).
Optional step for more tender beef (skip if you're in a rush): Add 1 tsp cornstarch, 1 tsp baking soda and 2 tbsp soy sauce to sliced steak. Toss to combine and let marinate for 30 minutes in a large bowl or Ziploc bag.
Heat sesame oil in a large skillet over med-high heat. Add steak, garlic, salt and pepper, sauteeing for 2-3 minutes until seared. Remove from heat and transfer to a plate. Meanwhile, mix stir fry sauce ingredients together in a small bowl.
Without wiping pan clean, add broccoli and carrots, then cover skillet with a lid. Cook for 3-4 minutes until veggies are tender, stirring occasionally. Add in baby corn and red pepper, sauteeing another 2 minutes.
Add steak back to pan, along with stir fry sauce, tossing well to coat. Cook 1-2 minutes until sauce thickens slightly.
Serve overtop of rice and garnish with sesame seeds. Enjoy!