Wash and slice the plums and discard the cores. Heat a large skillet over medium heat and add the plums. Fry, stirring occasionally until lightly browned, about 3-5 minutes. Add the coconut oil and stir to coat. Fry for another 3-5 minutes until the plums begin to soften. Add 2 tablespoons of coconut sugar, stir, and reduce the heat. Cook for another 5-7 minutes, until the plums release their juices and begin to caramelize slightly with the sugar. The plum juice should be brownish-bordeaux in color and slightly sticky, resembling syrup in consistency. Remove from the heat and set aside.
Put the rice and milk into a large pot. Stir everything well, then place the pot over very low heat. Cook gently for about 25 minutes, stirring frequently. Add the remaining coconut sugar and cook, still stirring, for another 20 minutes or until thick and creamy.
Transfer the coconut risotto to four glasses or small bowls and top with plums and sauce.