Preheat the oven to 350°F (175°C). Remove the outer papery skins from the garlic heads, leaving the cloves intact. Slice off the top quarter of each head to expose the cloves. Wrap tightly in foil and roast until very soft and fragrant, approximately 60 minutes. Remove from the oven and allow to cool for about 10 minutes, then squeeze the roasted cloves from their skins and set aside.

While the garlic roasts, heat the olive oil and sliced garlic in a small skillet over medium-low heat. Cook gently, stirring occasionally, until the garlic turns golden brown, about 15 minutes. Using a slotted spoon, transfer the garlic slices to a paper towel–lined plate. Reserve the infused oil for later use.

In a small bowl, combine the lemon juice and water. In a separate bowl, whisk together the tahini and the reserved garlic-infused oil until smooth and fully emulsified.

In the bowl of a food processor, combine the chickpeas, roasted garlic, minced garlic, salt, and cayenne pepper. Process until the mixture is finely ground, about 15 seconds. Stop and scrape down the sides of the bowl.

With the processor running, slowly add the lemon juice and water mixture through the feed tube in a steady stream. Stop and scrape the bowl, then process for 1 minute. With the processor running again, gradually add the tahini mixture. Continue processing until the hummus is smooth, creamy, and well blended.

Transfer the hummus to a serving bowl. Top with the reserved toasted garlic slices and minced parsley. Cover and allow the hummus to rest at room temperature for at least 30 minutes to allow the flavors to fully develop. Drizzle with additional olive oil before serving, if desired.