Add all of the ingredients, except the olive oil and warm water, to a food processor or a high-speed blender. Pulse until you have a smooth consistency. Note: You can absolutely use either a food processor or a high-speed blender here!: You can absolutely use either a food processor or a high speed blender here! : The moment you pulse the basil , spinach , pine nuts , garlic , salt, pepper and optional parmesan cheese , you will first notice a coarse, leaf flecked mash that soon turns more cohesive. Listen for the change from loud chopping to a more even, lower hum, and watch the color shift from a dull green to a bright, glossy emerald; that visual cue tells you the leaves are being properly broken down and oils are being released. Smell the mixture as it comes together; the aroma should be herb forward with a warm garlic note and a hint of toasted nut if you pre toasted. If the processor stalls, give it brief pauses to avoid overheating the motor and to push down ingredients with a spatula. A common mistake is over processing into a completely watery puree, which destroys texture. Stop when the paste is smooth but still has body, so you retain pleasant mouthfeel and aromatic intensity.
With the motor running, drizzle in the olive oil. If needed you can add in a tablespoon of hot water as needed to make a smooth pesto.: As you drizzle the extra-virgin olive oil slowly into the running machine, the mixture will emulsify and become glossy, like a dressing coming together. You should see the paste lighten slightly and hear the motor shift to a steady tone as the oil blends in; this is when the pesto gains silk and shine. If the mixture stays stubbornly thick, add a small amount of warm water to loosen it; warm water helps the emulsion integrate more readily than cold will. Pay attention to texture, aiming for a spreadable, spoonable consistency that clings rather than pours off a spoon. One frequent error is pouring oil too fast, which prevents emulsification and can leave the oil separated on top. Slow and steady results in a smooth, cohesive pesto that carries flavor evenly through your dishes.
Taste and adjust seasoning.: Right after the emulsion forms, give the pesto a careful taste for salt, pepper and acidity. You should sense bright herbaceous notes up front, a warm garlic mid palate, and a rounded oiliness from the olive oil . If it feels flat, add a pinch more salt; if it needs lift, add a dash of fresh lemon juice. If the garlic is too assertive, a little extra spinach or a touch more oil can mellow it. Texture wise, if it is too loose, a few extra pulses with a spoonful of nuts can thicken it. A classic misstep is to skip tasting until the pesto is already plated; seasoning at this stage ensures balanced flavor and prevents an overly salty or underseasoned finish.
Use immediately or store for up to 1 week in a tightly sealed container.: Fresh pesto has the brightest aroma and flavor when used right away, and it will look vibrantly green straight out of the blender. If storing, press a thin film of olive oil on the surface to slow oxidation and keep air out, then seal the container tightly. Refrigerated pesto will mellow and the flavor will integrate over a day, which some people prefer, but prolonged storage can darken the color. For longer preservation, freeze in ice cube trays and then transfer the cubes to a bag. A common mistake is leaving pesto loosely covered, which allows air to brown the surface and degrade aromatic quality.
