Preheat oven to 350˚F. Butter a bundt pan well.
Process/shred/finely chop the carrots.
In a mixing bowl, beat together oil, molasses, and sugar.
Beat in eggs until well combined. Then using a spatula, incorporate the carrots and (optional) walnuts and orange zest.
Combine all dry ingredients in a measuring cup or separate bowl.
Use a spatula to stir the dry mixture into the wet batter until just combined. Pour into pan.
Bake at 350˚F for ~40 min until springy to the touch.
While the cake is cooling, prepare the frosting. Make sure the cake is cool enough before frosting or the frosting will melt! For the frosting, beat together all ingredients until smooth. You may have to add a bit more confectioner's sugar as needed to reach your desired sweetness. If it is runny, refrigerate it for 15 minutes, then beat it once more before frosting.