1) Preheat oven to 180C/Gas 4. Grease and flour 3 (20-cm) round pans; Line bottom of the pans with greaseproof paper.
2) In a large bowl, combine flour, sugar, bicarbonate of soda, cinnamon, and salt. Add eggs and vegetable oil. Using a hand mixer, blend until combined. Add carrots and pecans, if using.
3) Pour into pans. Bake for approximately 40 minutes. Remove from oven and cool for 5 minutes. Remove from pans, place on greaseproof paper and allow to cool completely before frosting.
For the frosting:
1) Add all ingredients, except nuts, into a medium bowl and beat until fluffy using a hand mixer. Stir in the nuts. Spread frosting on top of each cake layer. Stack the cakes on a serving plate and serve.