In a large bowl, toss the beef with 1 teaspoon each salt and pepper to coat evenly.

In a large frying pan, heat the olive oil over med-high heat and, in batches, saute the beef until browned on all sides. Approximately 5 minutes.

Remove from pan and set aside.

Add the onion and garlic to the pan and saute for 1 minute over med-high heat.

Add the curry paste and stir until it coats the onion and garlic, approximately 30 seconds.

Deglaze the pan with the coconut milk, stirring and scraping up the browned bits on the bottom of the pan with a wooden spoon.

Stir in the fish sauce, lime juice and brown sugar and heat to boiling.

Transfer the beef to the slow cooker and add the coconut milk mixture.

Cover and cook until the beef is tender and the sauce is thickened, approximately 3 hours on the high setting or 6 hours on the low setting.

Serve immediately.