Preheat the oven to 340°F (fan).
Melt the butter and pour it into the bottom of a lined 9.5-inch springform cake tin. Cover with brown sugar and arrange the sliced pears. Set aside.
Mix together the milk and vinegar. Set aside for 10 minutes.
Add the remaining wet ingredients to the milk mixture.
Sift in the dry ingredients and gently mix until just combined.
Pour the batter into the tin over the pears and bake for 40-50 minutes, or until well risen and cooked through.
Flip the pan onto a serving plate and leave to cool before slicing. Enjoy!