In a mixing bowl or pint container, combine the 1 ¼ cup whole milk, 1/2 cup heavy cream, 3 tablespoons dry vanilla ice cream mix, 2 tablespoons granulated sugar, 2 tablespoons lemon juice, and 1 teaspoon lemon zest. Whisk until the sugar and ice cream mix are fully dissolved.
Pour the lemon mixture into the Ninja Creami pint container, secure the lid, and freeze for 24 hours.
After freezing, remove the pint from the freezer, take off the lid, and place it in the Ninja Creami. Select the "Gelato" function and churn until smooth.
After the first churn, make a small well in the center of the gelato and add the 2 tablespoons raspberry preserves or puree. Use the "Mix-In" function to gently incorporate the raspberry swirl.
Serve immediately for a fresh, soft gelato with a beautiful swirl, or refreeze for a firmer consistency.