Step 1Preheat oven to 160°C. Lightly grease a 24cm springform pan. Line base and sides with paper, extending paper 3cm above top of pan.
Step 2Beat butter, sugar, vanilla and zest with an electric mixer until well combined. Add eggs one at a time, beating well after each addition. Fold in sifted dry ingredients and cream in two batches. Fold in rhubarb. Spread mixture into prepared pan and sprinkle evenly with combined extra sugar and cinnamon.
Step 3Cook for about 1 hour 15 minutes, or until cooked when tested with a skewer. Cover top with foil if sugar starts to over brown.
Step 4Remove cake from pan and cool on wire rack. Cake is delicious served warm or cold with custard or cream.