Mix in the dry ingredients into the wet alternating with the sour cream. Alternating dry ingredients and sour cream, mix in 1/3 of the dry ingredients into the wet, followed by ½ of the sour cream. Repeat until all the ingredients are just combined.
Make the cream cheese frosting. Beat the butter and cream cheese on medium speed until smooth and creamy. Beat in the vanilla extract, powdered sugar, salt and 1 tablespoon (15 ml) milk until smooth and well combined. If needed, add up to 3 tablespoons additional milk.
Place the first carrot cake layer on top. Apply half the frosting to the first layer of the carrot cake. Smooth evenly across and slightly passed the top onto the side. Top the cream cheese frosting frosting with the second layer of carrot cake. Apply the rest of the cream cheese frosting to the top, smoothing it out to the edge of the cake. Top the cake with chopped pecans if you like.