Put the garlic in a small oven safe dish, and cover it with the oil. Cover dish with foil and bake 350F for about 40-50 minutes, or until the cloves are soft and lightly caramelized in color. .
Allow to cool to room temperature, then strain the garlic in a fine mesh strainer or cheesecloth, reserving the oil (can be stored in an airtight container in the refrigerator). Can keep the cloves whole, make a chunky smashed garlic using a fork, or use a whisk to mash until totally smooth (I’m a fan of the chunky smash). Store the roasted garlic in an airtight container in the fridge.
For the Tri-Tip:
In a mixing bowl, whisk all ingredients except for the tri-tip and oil well to combine. While continuing to whisk, slowly stream in the oil to emulsify and thicken. Reserve.
Using a large fork, pierce the tri-tip all over to help tenderize, as well as to create mini channels for the marinade to soak up into. Please the roast in a 1 gallon zip-top bag, and then pour marinade into bag. Remove as much excess air as possible, and then seal bag. Massage the roast in the bag to make sure the meat is fully coated in the marinade. Place in refrigerator and let marinate for 5-6 hours.
About 30 minutes before you are ready to cook, remove the meat from the bag , allowing as much of the excess oil to stay behind in the bag. Leave the meat on a plate lined with paper towels, so that residual marinade will drain off. You can now also preheat your grill to high (if using gas), with the cover closed to help the inside of the grill get as hot as possible.
Now that the meat has “tempered” (taken off the chill from the fridge), pat any residual marinade dry with a paper towel, then liberally season all sides of the roast with salt & pepper. Carefully place meat onto the grill, close the lid, and cook on high for 5-7 minutes, or until a good sear with visible grill marks. Flip meat over, close the lid, and grill the other side and additional 5-7 minutes. Reduce the flame directly under the roast to low, and keep the other side of the grill at medium. Flip the roast back to the first side, then close the grill and cook an additional 8-10 minutes (4-5 minutes on each side). A 2-pound roast will need about 20-25 minutes of total cooking time - but play it safe and use an instant read thermometer to check the temperature, pulling it from the grill when the thickest part reaches 130°F.
Pull the roast to a rack or cutting board and let it rest for 15-20 minutes. This is when the meat juiced redistribute themselves, SO DON’T RUSH IT! Slice the roast against the grain, adjusting the angle you are slicing at as the muscle fibers start to change directions near the middle.