First make the crepes following this recipe. If under time pressure, you can also make the batter a day ahead or make crepes the evening before making the cake, although fresh crepes give better flavor.
Make the candied oranges: Place sliced oranges in a medium saucepan (I use enamel) and cover with water. Bring to a simmer over medium heat and cook like that for 10 minutes, you’ll notice the oranges will get softer. Remove from heat and drain well.
Return oranges back to the saucepan, add 1 1/2 cups water and sugar, stir until dissolved. Bring to a simmer and cook for about 10 minutes, until oranges are tender and paler in color. Remove from water and let cool.
Make filling: In a bowl, combine ricotta and marmalade. Stir just until incorporated, taste and start adding the sugar. I needed about 1/2 cup, although the amount can depend on your taste and how sweet the marmalade is.
Assemble the cake: Start by placing one crepe on a large plate. Spread about 3 tablespoons ricotta mixture all over, top with another crepe and gentle pat it down. Top with 3 tablespoons ricotta, another crepe and continue in this manner until you run out of crepes. If you have any ricotta left, spread all over the top of the cake. Then top with candied orange slices and chill cake for about 30 minutes before serving, which will give ricotta time to set.
Serve with both a knife and a fork, store leftover cake covered in the fridge and eat within a day or two.