Combine the garlic, olive oil, salt, pepper, and Essence together on a sheet of aluminum foil. Fold the edges of the foil together to form a tent and roast until just-tender, about 20 minutes. Set aside to cool before removing the cloves from their skins. Try to keep the pretty, intact cloves for stuffing the olives, and use the other cloves for another purpose.
If the olives you have purchased are already stuffed with pimientos, remove the pimientos and reserve for another purpose. Carefully stuff each olive with 1 of the roasted garlic cloves and return the garlic-stuffed olives to the jar with the brine. Allow to sit in the brine for at least 2 weeks before using.
After the olives have "matured," for each martini combine 1 2/3 ounces of the gin with 1/3-ounce of the vermouth over ice in a cocktail shaker and shake until thoroughly chilled. (Add olive brine to taste, if desired.) Strain into a martini glass and garnish with a toothpick that has been skewered with 2 of the garlic-stuffed olives.