Whisk together the evaporated milk and beaten egg yolks
Cook in a double boiler over simmering water, stirring constantly until the mixture thickens and coats the back of a spoon and reaches a temperature of 160 degrees. About 15 minutes
Pour into a blender, add cream of coconut, sweetened condensed milk, tequila, water and vanilla extract
Blend on low speed about 30 seconds until combined
Transfer to quart jars, seal and refrigerate overnight to give the flavors time to meld
Shake before serving to ensure it remains homogenous