Heat the oven to 180C. Line with baking paper a 22cm square baking tin.
Roast the walnuts all 75gr (that can be done days in advance) at 180C for up to 10 minutes.
Place in the pot with the mandarin juice and honey, place over medium heat and add Dutch carrots as soon as honey is dissolved. Cook for 3-5 minutes making sure not to overcook the carrots as they need to still be firm when you take them out. Leave the pot with the juice on the stove for another 3-5 minutes – to reduce it. At the end, add roasted walnuts. Leave to cool.
In a large mixing bowl whisk eggs with sugar until very fluffy and the colour changes a bit, not much though since we are using dark brown sugar. Add honey and vanilla (vanilla paste can be used as well and in that case use 1 teaspoon) and whisk on a low speed just to combine. Increase the speed on your mixer and slowly add olive oil, making almost a mayonnaise that way. Fold in flour mixture, add grated carrots and fold gently again. At the end add 50 gr of walnuts and fold one more time.
Serve a piece of cake on a plate with some whipped cream topped with mandarin syrup and roasted walnuts.