This rich and flavorful hors d'oeuvre spotlights the earthy truffle.
Process egg yolks and garlic in a food processor until combined. With machine running, add canola oil drop by drop until mixture begins to emulsify. Add remaining canola oil and the olive oil in a slow, steady stream, and process until mixture is very thick and creamy. Transfer to a small bowl; stir in lemon juice. Season with salt and pepper. If mixture is very stiff, stir in up to 2 teaspoons cold water. Aioli can be refrigerated in an airtight container up to 1 day.
Prepare an ice-water bath; set aside. Bring a large pot of water to a boil; add 1 tablespoon salt. Add cauliflower, and cook just until crisp-tender, 2 to 3 minutes. Using a slotted spoon, transfer cauliflower to ice-water bath to stop the cooking. Drain in a colander, and pat dry with paper towels. Cauliflower can be refrigerated in an airtight container up to 2 days.
Cut cauliflower florets in half lengthwise. Top each floret with 1/2 teaspoon aioli and a truffle slice. Serve.