Roasted Garlic Mayonnaise:

1. Preheat your oven to 400°F.
2. Slice the top off of the garlic head to expose all the cloves and place the garlic on a sheet of aluminum foil, cut side up.
3. Drizzle olive oil over the top of the garlic, making sure to coat all the exposed cloves.
4. Bring the edges of the foil together and crimp, making a foil packet to seal in the garlic and place on the middle rack of the oven with a baking sheet beneath the garlic foil packet to catch any leaks.
5. Bake for 30-40mins, until the garlic cloves are soft to the touch. Let the garlic cool to room temperature.
6. Squeeze the garlic cloves into a medium bowl and mash into a paste with the back of a spoon.
7. Add the mayonnaise and mix until the roasted garlic paste is incorporated into the mayonnaise.
8. Cover and refrigerate until ready to use.

Assemble the sandwich:

1. Generously spread the garlic mayo on both sides of each roll and sprinkle with a little kosher salt and freshly ground pepper.
2. Place 1/4 pound of the sliced tri-tip on each roll bottom and top with baby arugula and pickled red onions.
3. Place the top slice of roll on the sandwich and dig in!