Crock Pot Beef Curry

2 1/2 to 3 lbs lean beef, cubed
2 tbs canola oil
2 large cooking onions, sliced
5 medium red skinned potatoes, scrubbed and cubed
3 tbs Patak’s (or other) brand mild curry paste
1 tbs Patak’s (or other) brand vindaloo paste
water to cover
1/2 cup white vinegar
kosher salt/fresh ground pepper
Heat oil in a large skillet over medium-high heat. Add beef and sear on all sides. Transfer beef, along with onions, potatoes and curry pastes to bowl of a large crock pot. Add water, just to cover ingredients. Turn heat to high and simmer for at least 4 hours, until beef is very tender. Add vinegar and season with salt and pepper. Continue simmering for another half hour. Adjust seasoning to taste.
Serve curry with cooked basmati rice and/or warm Indian flat bread such as naan or chapatties.