Preheat your SousVide Supreme water bath to 134 degrees Fahrenheit
Pat dry your tri-tip and use one tablespoon of mustard on each side of the tri-tip and spread it around to ensure an even coating
Generously sprinkle your Caveman Rub over your entire tri-tip
Place your tri-tip in a vacuum seal bag, add your grass-fed butter, then vacuum seal
Submerge your tri-tip in the water bath for a minimum of two hours but you can leave it up to six with no issues
Once removed, pat dry your tri-tip and heat a cast iron skillet on your stove top or your grill to high heat (either works, just need high heat for a quick sear)
Sear each side of your tri-tip for approximately two minutes
Remove from the pan or the grill and slice against the grain