Meanwhile, cut beef into strips or cubes. Add olive oil to the frying pan and brown meat on high heat. (Depending on the size of your pan, you may need to do in 2 batches). Sprinkle with salt and pepper. Add onion about half way through searing. Sauté until translucent. There should be very little liquid left in the pan, if any. Sprinkle cornstarch and stir to mix. Next add tomato paste and garlic. Stir to incorporate and remove beef to oven proof casserole dish.