Preheat oven to 350°F/177°C. Grease two 8-inch cake pans with butter, line the bottoms with circles of parchment and grease the parchment.In a medium bowl, sift together the flour, baking soda, cinnamon, and salt. Whisk to combine, and set aside.In a large bowl, combine the sugar and walnut oil, and whisk until smooth and blended. Add the eggs, and whisk until combined. Gradually add the flour mixture, stirring until just combined. Then fold in the carrots until blended. Divide the batter evenly between the two cake pans, and bake until a toothpick inserted in the center comes out clean, about 40 to 45 minutes. Let the cakes cool for a few minutes in the pans, then invert the cakes onto wire racks, remove the parchment paper, and cool completely. Use immediately, or wrap tightly in plastic and refrigerate for up to 3 days.