Wash and thoroughly dry the shiso leaves. Remove any tough stems.

In a high-speed blender (like a Vitamix), combine shiso leaves, cashews, garlic, lemon zest, and olive oil.

Blend on low to start, gradually increasing speed until the mixture is smooth. Add more olive oil for a thinner sauce, or use less for a thicker spread.

Taste the pesto and adjust seasoning—add more salt or a splash of lemon juice if needed.

Transfer to an airtight container. Refrigerate for up to 1 week or freeze in small portions for long-term storage.