Step 1In a large saucepan, heat the hoji-cha and milk over medium-high, stirring occasionally to prevent scorching. Just before the milk boils, reduce heat to low and cook for 5 more minutes, stirring occasionally to allow the tea to steep. Remove from the heat. Strain the milk through a cheesecloth-lined fine-mesh strainer and return the milk to the saucepan. Set aside.
Step 2In a large bowl, combine the sugar and egg yolks with a hand mixer or whisk. Whisk until pale and thick, about 2 to 3 minutes (if using a hand mixer, slightly longer if by hand). Temper the milk into the egg mixture by whisking about a cup of milk at a time into the eggs to warm the eggs. Add the egg mixture to the saucepan and mix well with a whisk to incorporate.
Step 3Cook over low heat, stirring constantly and scraping sides with a rubber spatula, until mixture thickens and coats the back of a spoon. Do not boil or the yolks will curdle.
Step 4Strain the mixture through a fine-mesh strainer into a bowl set in another bowl filled with ice water and ice. Stir until cool. Pour the mixture into an ice cream maker and freeze according to the manufacturer's instructions.
Step 5Spoon the ice cream into a lidded plastic container, covering the surface of the ice cream with plastic wrap before covering with the lid. Freeze several hours until firm.