In a shaker or quart-size Mason jar, combine the fresh pineapple, cilantro and tequila. Muddle to break down the pineapple and cilantro.
Add the agave, pineapple juice, lime juice and a handful of ice. Place the lid on the shaker/jar, and shake vigorously for a minute to fully combine all ingredients.
Strain into an Old Fashioned glass with fresh cubed or crushed ice. Garnish with a piece of pineapple and sprig of cilantro.
Notes
Using a wide mouth quart-size Mason jar is great for muddling and shaking the ingredients if a shaker is not available. Shaking for a good minute allows the ingredients to fully mix and for the pineapple and cilantro to break down and infuse into the liquids.