With a vegetable peeler remove zest from Meyer lemons in large strips. Make sure that you peel only the colored part; the white part of the skin will impart a bitter taste. Combine lemon zest, water and sugar in a small nonreactive saucepan and heat over the medium heat, stirring constantly, until all sugar is dissolved. Reduce the heat and simmer for 2 minutes. Cool the mixture, strain and keep in a fridge.
In a Boston shaker, combine Arrogante Reposado, freshly squeezed Meyer lemon juice, Meyer simple syrup and Cointreau (orange-flavored liqueur). Add 3/4 cup of ice cubes. Shake vigorously and strain into a chilled cocktail glass, rimmed with kosher salt. Garnish with a Meyer lemon slice.