Preheat oven to 350°F. Grease an 8½ x 4½-inch loaf pan (or line with parchment).
In a large bowl, whisk together almond flour, hazelnut flour, arrowroot starch, flaxseeds, walnuts, tapioca starch, salt, and baking soda.
In a separate bowl, mix oil, eggs, coconut milk, yacón syrup, and vinegar.
Add wet ingredients to dry and stir until just combined (don’t overmix).
Pour into prepared pan and bake for 40–45 minutes, until a toothpick comes out clean.
Cool before slicing. Store in the fridge for up to 5 days.