In a pitcher, combine boiling water, Thai tea mix and sugar. Let steep for 15 minutes and strain into a clean container. Allow tea to cool completely, then cover and refrigerate until ready to serve. Fill 5 tall glasses with ice, add tea till glass is 3/4 full. Add cream of your choice, starting with about 1 1/2 tablespoons cream, adding more until desired balance is reached. Serve immediately.