Preheat oven to 325°F (160°C). Grease a loaf or cake pan generously with cooking spray and set aside.
Peel the plantains, slice them, and then puree them in a food processor or blender until creamy with no lumps.
Add the eggs, yogurt, sugar, butter, vanilla extract, and milk, and mix well.
Combine flour, salt, baking powder, baking soda, optional lime zest, and nutmeg.
Add the dry ingredients to the batter and stir well, scraping the sides of the mixing bowl as you go.
Pour the cake batter into the greased loaf pan (or cake pan). Add a couple of plantain slices and sprinkle with brown sugar if desired.
Bake at 325℉ (160℃) until a tester inserted into the middle of the loaf comes out clean, 45-50 minutes. Transfer it to a wire rack and allow it to cool.
Melt the butter and brown sugar until bubbling and lightly browned. Pour in rum and vanilla extract, and simmer until slightly thickened and it bubbles. Pour it over the freshly baked bread, and enjoy.