Preheat your oven to 180°C and line a cupcake tin with cupcake liners. Grease the liners with a bit of oil so they can come off easily from the cupcake.
In a mixing bowl, mix the flour, sugar, baking powder, baking soda, salt and vanilla. Set aside.
In a another bowl, mix the milk with white vinegar and cornstarch until cornstarch is fully dissolved. Add the oil and mix until incorporated.
Add the wet to the dry ingredients and mix everything until a smooth batter forms.
Start by adding 1 tbsp of batter into each cupcake liner, followed by 1/2 tbsp berries jam, followed by 2 tbsp batter. Decorate with a bit of jam on top (optional).
Bake in preheated oven for 25-30 mins or until the top of the cupcakes is firm to touch.