2 cups milk
1/2 cup white sugar, or to taste
1/2 teaspoon salt
2 egg yolks
1 slice lemon rind
1 teaspoon vanilla extract
Heat cornstarch in a pot over medium heat. Stir in milk slowly. Add sugar and salt. Cook and stir until slightly thickened, about 15 minutes. Whip egg yolks in a bowl. Stir in 1/4 of the cornstarch mixture. Transfer the egg-cornstarch mixture to the pot. Cook and stir until combined, about 1 minute. Add the lemon rind; cook and stir until thickened, 7 to 10 minutes. Remove from heat; add vanilla extract and mix well.