The secret ingredient in many professional layer cakes and a kind of magic to the home baker is called simple syrup and it’s precisely that: a syrup made simply of equal parts water and sugar.

This dense, syrup-soaked cake is a triple orange threat, full of zest, juice and whole slices of candied orange. For the cake: Heat the oven to 350 degrees. Butter a 9- to 10-inch springform pan and ...