Preheat your oven to 400°F (200°C).

Slice off the top of the garlic heads to expose the cloves.

Drizzle with a bit of olive oil, wrap in aluminum foil, and roast for 35-40 minutes, until the cloves are soft and golden brown.

Allow the garlic to cool, then squeeze the roasted garlic cloves out of their skins.

While the garlic is roasting, toast the walnuts in a dry skillet over medium heat for about 5-7 minutes, stirring occasionally, until fragrant. Let them cool slightly.

In a food processor, combine the roasted garlic, toasted walnuts, basil leaves, and Parmesan cheese. Pulse until the ingredients are finely chopped.

With the processor running, slowly drizzle in the olive oil until the pesto reaches your desired consistency. You can add more olive oil if you prefer a thinner pesto.

Taste and adjust seasoning with salt, pepper, and lemon juice.

Use immediately or store in an airtight container in the fridge for up to a week. You can also freeze the pesto in ice cube trays for longer storage.