In a saucepan, mix egg yolks and sweetener until creamy.
Slowly add the partly skimmed evaporated milk until mixed thoroughly. Heat the mixture on medium until it thickens. Ensure the mixture's temperature reaches above 165°F to cook the egg yolks and avoid salmonella poisoning. Do not boil, but let it gently heat through.
Use a strainer to sieve the matcha tea powder straight into the custard base, then whisk until thoroughly combined. Alternatively, use a Japanese bamboo whisk (Chasen) in a small bowl to combine the matcha with a few tablespoons of custard before adding it to the saucepan.
Whisk the custard base vigorously until smooth and turns into a vibrant green colour. Allow it to cool, then cover the saucepan with a lid, or plate and place it in the fridge to chill for at least 30 minutes.
Make the whipped cream: Place whipping cream and sweetener into a mixing bowl. Use an electric mixer with a whisk attachment to beat the mixture until it doubles in size and becomes fluffy. Then, mix in the vanilla extract until it is well incorporated.
Fold the chilled Matcha custard base into the whipped cream and mix by hand or with an electric whisk on low speed. Transfer the blended mixture into a freezer-proof container.
Freeze the ice cream mixture overnight, stirring every 30 minutes for the first 2 hours. This will smooth the ice cream and prevent it from turning rock hard.
The next day, or when ready to serve, let the ice cream sit out for a few minutes before scooping and serving.