Preheat oven to 350°F (180°C). Grease and line the base and sides of two 8.5" x 4.5" loaf tins.Put the softened butter, sugar and vanilla in a large bowl and use an electric mixer to beat until pale and creamy. Add eggs, one at a time, beating well after each addition. Stir in flour and milk alternately until just combined.Spoon evenly between prepared pans and smooth the surface. Bake in oven for 30 minutes or until a skewer inserted in the centre comes out clean. Remove from oven.Combine the cinnamon and extra sugar in a small bowl. Turn the cakes onto a wire rack and evenly brush with extra butter. Sprinkle with cinnamon sugar. Serve warm or at room temperature.