Add fresh basil leaves, toasted pine nuts, garlic, and kosher salt to the bowl of a food processor fitted with the blade attachment.
Pulse the ingredients until the basil leaves are finely chopped and all the ingredients are well combined.
Add the freshly grated Parmigiano Reggiano and Pecorino Romano cheeses to the mixture.
Pulse again until everything is evenly distributed.
With the food processor running, slowly pour in the extra virgin olive oil in a steady stream.
Continue to process until the sauce reaches a smooth and creamy consistency.
Combining the Butter and Pesto
Add the softened butter to the bowl of the food processor.
Process until the butter is fully combined with the pesto, creating a smooth and creamy pesto butter.
Forming and Setting the Pesto Butter
Transfer the pesto butter onto a piece of plastic wrap.
Shape it into a log, wrap it tightly, and refrigerate until set, about 1-2 hours, OR use it softened as is.
Notes
Butter Softening - Make sure the butter is softened to room temperature before combining it with the pesto. This ensures it blends smoothly and evenly. If you forget to take it out of the fridge in advance, you can cut the butter into small pieces and let it sit out for about 10-15 minutes to soften.Grating Cheese - For the best texture, grate the Parmigiano Reggiano and Pecorino Romano cheeses yourself rather than using pre-grated cheese. Pre-grated cheese often contains anti-caking agents that can affect the consistency of your pesto butter.Forming the Log - When shaping the pesto butter into a log, use plastic wrap or parchment paper for an easy and mess-free process. Tightly wrapping it ensures it holds its shape while refrigerated.