Preheat oven to 160 C / Gas mark 3. Lightly grease two 23x13cm (9x5 in) loaf tins.
In a small bowl, stir together milk, lemon juice and vanilla; let stand for 10 minutes.
In a large bowl, mix together 225g brown sugar, oil and egg. Combine the flour, salt and bicarbonate of soda, and stir into sugar mixture alternately with the milk mixture just until combined. Fold in rhubarb and nuts. Pour batter into prepared loaf tins.
In a small bowl, combine 4 tablespoons brown sugar, cinnamon and butter. Sprinkle this mixture over the unbaked loaves.
Bake in preheated oven for 40 minutes, until a skewer inserted into centre of a loaf comes out clean.
Delicious! This was pretty easy to make and very lovely to eat, still slightly warm. I used flaked almonds instead of walnuts, and this went very well with the rhubarb. I did find it took over 1 hour to set in the oven, rather than 40 minutes, but this may be due to an old oven. I will be making this again.
This was very tasty and a great way to use up Rhubarb. We have a nice supply from the garden and this Cake/Bread went down a treat. The Rhubarb is somewhat 'disguised' and you would not know it was in the bread unless someone told you, which is perfect as my family say they don't like Rhubarb but they love this! But I found it better not to melt the butter for the topping and just to rub it into the sugar and cinnamon. This will be a regular bake.