Line a 8 x 4 1/2-inch loaf pan (a 9 x 5-inch would also work but obviously the semifreddo will be a bit more stout) with parchment paper, leaving some extra for overhang. The overhang will help remove the semifreddo after it’s frozen.
There are a few different ways you can brew the thai tea leaves. Since they’re really small, I used a chemex. If you have a pour over situation, you can use it. You could also use a drip coffee maker. I placed my thai tea leaves in the filter of my chemex and poured in 1/2 cup of boiling water. When it went through, I poured it out into a measuring cup and ran it through the tea a second time. (I wanted super strong tea.) You should end up with about 1/4 cup of very strong thai tea. Set aside and cool to room temperature.
To a stand-up mixer with the whisk attachment (a hand-mixer would also work), pour in the heavy cream, sweetened condensed milk and salt. Beat for until soft peaks form, about 2 to 3 minutes. Make sure not to walk away because this mixture can be over-beaten. When you’re at soft peaks, pour in the thai tea and beat until just combined. Transfer the parchment-lined loaf pan and transfer to the freezer for at least 6 hours, ideally overnight.
Allow to stand for about 5 minutes and then remove by lifting up the overhang pieces of parchment. Invert onto a serving board and slice up. Top with a sprinkling of toasted coconut.