Prep the loaf pan. Preheat oven to 375 F and place rack in the middle of the oven. Spray a loaf pan with nonstick baking spray, then set aside.
Combine the dry ingredients. Sift together 6.3 oz (~1 ⅓ cups) flour, 2 tsp baking powder, 1 ½ tsp ground cinnamon, and ½ tsp Kosher salt, then set aside.
Finely grind in the walnuts. To grind walnuts, either place in the bowl of a food processor and pulse until a fine powder or place in a sealed Ziplock bag and smash with a rolling pin. Place 2.5 oz (½ cup) crushed walnuts in a small bowl with ⅓ cup raisins, then toss with remaining 1 Tbsp of flour and set aside.
Prepare the wet ingredients. In the bowl of a stand mixer (or using a hand mixer), beat ¾ cup brown sugar and 3 eggs together on medium speed until very shiny and smooth, about 5 minutes. With the mixer still running, slowly drizzle in 1 ¼ cup canola oil and 1 Tbsp vanilla. Scrape down the sides as needed.
Fold in the dry ingredients. Carefully fold the flour mixture into the wet ingredients until just combined. Add finely ground nuts, raisins, and 1 ½ cups grated carrots, then fold once more until evenly distributed.
Bake the carrot loaf. Pour batter into prepared loaf pan, then bake for 60-70 minutes, or until evenly browned and a cake tester inserted into the middle of the loaf comes out clean with few crumbs.
Cool, then serve. Place pan on a cooling rack and let sit for 10 minutes, then remove loaf from pan (it should release easily when turned over) and place on the rack to cool completely.
Make the cream cheese frosting. In the bowl of a stand mixer (or using a hand mixer) beat 8 oz room temperature cream cheese and 8 Tbsp softened butter on high until very smooth and completely blended, about 2 minutes. Add 2 tsp vanilla extract and a generous pinch of Kosher salt, then reduce speed to low and slowly add 1 cup sifted sugar. Continue to beat until sugar is incorporated and frosting is creamy, about 2 minutes.
Serve with cream cheese frosting. Spread a generous even layer of cream cheese frosting on top of the cooled carrot cake loaf. Serve with additional frosting, as desired.