For tenderising the beef, add the baking soda (bicarbonate of soda) to the beef pieces, mix and rub well. Rest on benchtop for 30 minutes. Then wash thoroughly and drain.
Combine the tenderised beef pieces with the marinade in a large bowl and mix well.
Prepare and mix the sauce ingredients except the potato starch mixture in a separate bowl. Set aside.
Heat up a non-stick wok with 4 tablespoons of extra virgin olive oil, pan-fry the beef on medium heat for 2 minutes on each side or until browned. Remove beef and set aside.
Add another 4 tablespoons of oil to the wok, then add garlic, ginger, and ground black peppercorn and stir-fry until black peppercorns are aromatic and garlic is lightly golden on low heat.
Add all the capsicums, onion, spring onions (shallots) and medium dry sherry and stir-fry for 1 minute on high heat.
Return the beef to the wok and stir-fry for another 2 minutes on high heat.
Then add the sauce mixture prepared in step 3 and stir-fry for 2 minutes on high heat.
Add the potato starch mixture and bring to a boil. Continue to stir-fry until the sauce thickens and the dish is heated through.