01 - Rinse the strawberries thoroughly, remove the green hulls, and cut each berry in half. Arrange the strawberry halves evenly in a rectangular mold or loaf pan (approximately 8 x 4 inches), ensuring they are distributed in a single layer.
02 - In a small saucepan, combine the 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. Once simmering, continue cooking for exactly 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 throughout the milk mixture.
05 - Let the milk mixture cool for 2 to 3 minutes until slightly thickened but still pourable. Gently pour the liquid over the arranged strawberries in the mold. Lightly tap the mold on the counter to release any trapped air bubbles and ensure the strawberries remain evenly distributed.
06 - Allow the yokan to cool completely at room temperature, then refrigerate for at least 3 hours or until fully set and firm to the touch.
07 - Once fully set, carefully unmold the yokan onto a cutting board. Slice into rectangular portions and garnish with fresh mint leaves if desired. Serve chilled.