Place cream and milk in a medium sauce pot. Set over medium heat and bring to a boil. Remove from heat and add tea leaves. Cover and allow to steep for 15-20 minutes. Strain out tea and discard.
Let tea-infused cream cool slightly. Transfer to a medium bowl. Add egg yolks, salt, and granulated sugar. Whisk until sugar has dissolved.
Add about 1 ½ cups of water to slow cooker. Place four 6-oz ramekins (or disposable aluminum foil ramekin cups) in slow cooker. Fill cups with custard mixture. Make sure that the ramekins are at least half submerged in water. If necessary, add more water in the bath.
Cover slow cooker with lid. Set to cook on low heat for 2-3 hours until custard has set and registers 185° F on a food safe thermometer.
Carefully remove ramekins from slow cooker water bath. Let sit at room temperature for about 10 minutes to cool. Then place in the fridge uncovered to cool, about 60-75 minutes. Once custard has completely cooled, cover with plastic wrap.
When ready to serve, remove chilled custard from the fridge. Let sit at room temperature for 15 minutes. Sprinkle about 1 tsp of superfine sugar over custard. Gently rotate ramekin around to ensure sugar is evenly distributed. Using a kitchen torch, melt and caramelize the sugar until a nice golden crust has formed. Let sugar cool slightly before serving.