Preheat oven to 180 degrees C. Grease and flour an 20cm square pan. Combine the flour, brown sugar, cocoa powder, bicarb soda and salt in prepared pan. Mix well with a fork.
Make three "wells" in the dry ingredients. Pour oil in the first, vinegar in the second, and vanilla in the third. Pour milk over the top and mix all ingredients with a fork until well blended. Pour chocolate chips over the top.
Bake in the preheated oven for 30 minutes, or until a toothpick inserted into the centre of the cake comes out with moist crumbs. Cool in pan for 15 minutes, then cut and serve directly from the pan.