Step 1: Preheat your oven to 350°F (175°C) and thoroughly grease a 10-inch bundt pan with baking spray or a butter-flour paste.
Step 2: In a large bowl, cream together the softened butter and granulated sugar until the mixture is light and fluffy, about 3-5 minutes.
Step 3: Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract and sour cream until smooth.
Step 4: In a separate bowl, whisk together the flour, baking soda, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Step 5: Divide the batter into three equal portions (approximately 2 cups each).
Step 6: Leave the first portion as vanilla. To the second portion, fold in the strawberry puree and optional food coloring. To the third portion, whisk in the cocoa powder and 2 tablespoons of milk.
Step 7: Spoon the chocolate batter into the bottom of the prepared bundt pan and smooth the top. Carefully spoon the vanilla batter over the chocolate, followed by the strawberry batter.
Step 8: Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Step 9: Allow the neapolitan bundt cake to cool in the pan for 15 minutes before inverting it onto a wire rack to cool completely.