Use an electric mixer or balloon whisk to mix together the yoghurt, eggs, oil and vanilla essence. Mix in the sifted sugar, flour and baking powder until the mixture is smooth. Stir in the rolled oats, white chocolate chips and almost all of the plain ones. Spoon the mixture into the prepared muffin tins and sprinkle the extra chocolate chips on top.
Bake in the preheated oven until the centres of the muffins are springy to the touch. Remove from the oven and serve while still warm.