Pour the heavy cream into a medium saucepan, and place it over medium heat until it starts to steam, making sure it doesn’t boil. Add the Thai tea leaves into the cream, give it a stir, then take it off the heat and cover the saucepan with a lid, letting it steep for at least 30 minutes. Then, strain out the tea leaves, and put the flavoured cream in the fridge for 30 minutes, until completely chilled.
Line a loaf tin or medium mold (I used a 20 x 10 x 6cm one) with plastic wrap. (You can grease the insides of the mold to make sure the plastic wrap sticks.)
Once the cream is chilled, add the vanilla extract to it, and whip it up to stiff peaks. Then keep it in the fridge.
Make a sabayon by first putting the eggs, sugar, salt into a medium bowl (or the bowl of a stand mixer). Then, place the sabayon over a bain marie (essentially a steam bath/a pot of constantly simmering water), making sure the bottom of the bowl isn’t touching the water. Heat this to 75°C (167°F) while continuously stirring it with a spatula, making sure it doesn’t cook or set at the bottom of the bowl. Once you’ve reached 75°C (167°F), whisk the liquid (either with a hand mixer or stand mixer) until it turns thick and ribbony. This will take 4-6 minutes.
When done, fold the whipped cream into the sabayon in 2-3 batches, making sure not to deflate the mixture too much. Pour the combined mixture into the lined loaf tin, and freeze it for at least 2 hours until completely solid.
When the semifreddo has frozen completely, take it out of the mold, remove the plastic wrap, and slice it into 1-inch thick pieces. Pour the toasted coconut flakes onto a tray or plate, and completely coat each piece of semifreddo in the coconut flakes. Once coated, pop them into the freezer for a final 15 minutes to set.
You can eat the semifreddo once they’re set, or keep them in an airtight container in the freezer for up to 2 weeks, and have them whenever you’re feeling peckish!