1. Preheat oven to 180C (360F). line an 9-inch (22-23cm) springform pan with parchment paper and grease with butter.
2. In a large bowl mix flour, oats, cinnamon and sugar. In a separate bowl grate carrots and mix them with fresh lemon juice. set aside.
3. For the first cake layer: grate 2 tablespoons (30g) cold butter on the bottom of the pan, sprinkle 3-4 tablespoons of the oat mixture, then lightly press. Evenly spread 1/3 of the shredded carrots, then sprinkle some raisins and crushed walnuts. Repeat the same process 2 more times: oat mixture (1/3 of the remaining), carrot mixture, raisins, walnuts, oat mixture, carrot mixture, raisins, walnuts, oat mixture. Finely, grate the remaining 100g cold butter on top of the cake, sprinkle 1 tablespoon sugar.
4. Bake for 35-40 minutes, until golden brown on top. Let cool for 20 minutes, release from the pan and let cool completely.