Prepare the Raspberry Puree: In a medium-sized saucepan over medium heat, combine the raspberries, sugar, and water. As the mixture warms, gently mash the berries with a fork or potato masher to release their juices. Allow the mixture to simmer for about 5 minutes, stirring frequently to prevent sticking.
Strain the Raspberry Juice: Pour the cooked raspberry mixture through a fine mesh strainer into a shallow bowl, pressing down on the solids with a spatula to extract as much juice as possible. Aim to collect about two-thirds to three-quarters of a cup of vibrant raspberry juice. Cover and place it in the refrigerator to chill completely.
Melt and Mix White Chocolate Base: Place half of the chopped white chocolate (4 ounces) into a microwave-safe bowl and heat in 20-second intervals, stirring each time until fully melted and smooth. Stir in the sweetened condensed milk and vanilla extract until the mixture is fully combined and silky. Chill this white chocolate mixture in the refrigerator until it cools completely.
Whip the Cream: Using a stand mixer fitted with a whisk attachment, beat the heavy cream on medium-high speed until stiff peaks form. This means the cream should hold its shape firmly when the whisk is lifted.
Combine White Chocolate Mixture and Whipped Cream: Pour one-third of the cooled white chocolate mixture into the whipped cream and gently mix to combine. Then, carefully fold in the remaining white chocolate mixture, making sure not to deflate the whipped cream for a light and fluffy texture.
Prepare Raspberry and White Chocolate Custards: Scoop out half of the combined custard into a separate bowl. Gently fold the chilled raspberry juice into this half, blending until just incorporated to create the raspberry custard. The remaining half remains the white chocolate custard.
Layer and Swirl Ice Cream: In a freezer-safe container, spoon alternating layers of the raspberry custard and the white chocolate custard. Sprinkle some of the remaining chopped white chocolate pieces over each layer. Once all layers are added, use a skewer or butter knife to swirl the layers in figure-eight motions to create a marbled effect.
Freeze Until Firm: Cover the container and place it in the freezer for at least 6 hours, preferably overnight, allowing the ice cream to set completely.
Serve and Enjoy: When ready to eat, scoop the ice cream into bowls or cones and savor the creamy, fruity delight!