01 - Rinse strawberries thoroughly, remove hulls, and cut each berry in half. Arrange the halves evenly in a rectangular mold or loaf pan (approximately 8 x 4 inches).
02 - In a small saucepan, combine whole milk, granulated sugar, and powdered agar-agar. Whisk vigorously until the agar-agar is completely dissolved and no lumps remain.
03 - Place the saucepan over medium heat and bring the mixture to a gentle simmer while stirring constantly. Maintain a gentle simmer for 2 minutes to fully activate the gelling properties of the agar-agar.
04 - Remove the saucepan from heat and immediately stir in the vanilla extract until evenly incorporated.
05 - Allow the milk mixture to cool for 2-3 minutes until slightly thickened but still pourable. Gently pour over the arranged strawberries in the mold. Lightly tap the mold on the counter to release trapped air bubbles and ensure even distribution.
06 - Let the yokan cool completely to room temperature, then refrigerate for at least 3 hours or until fully set and firm to the touch.
07 - Once fully set, carefully unmold onto a cutting board. Slice into rectangular portions and garnish with fresh mint leaves if desired. Serve chilled.