Place 1/2 cup milk in a medium mixing bowl and sprinkle with gelatin. Set aside to soften for 5 minutes. Bring remaining milk and evaporated milk to nearly a boil in a medium saucepan over medium heat, stirring often. Add 1/2 cup light brown sugar, cornstarch, and the egg yolks to the softened gelatin and whisk until blended. Gradually whisk about a 1/4 cup of the hot milk mixture into the gelatin mixture; repeat this process once or twice using about 3/4 cup of the hot milk mixture. Pour the warmed gelatin mixture into the saucepan with the hot milk and bring to a boil over medium-low heat, stirring constantly. Cook for a few minutes or until mixture is very thick and coats the back of a wooden spoon.