Cut pineapple into 1 inch thick rings. Discard rind and remove the pulp.
Preheat grill pan with 1/2 tablespoon of butter. Grill for 4-5 minutes on each side, or until lightly charred. Cool completely.
In a blender or large bowl, pour tequila, triple sec, grilled pineapple, lime juice, simple syrup,water, and vanilla extract.
Blend or muddle until smooth, then strain if desired.
Run a lime slice around the rim of the glass and dip in kosher salt.
Add some crushed ice to glasses. Pour in margarita.
Garnish with extra pineapple or lime wedges if desired.