The internet warned me that the ricotta should be drained as much as possible. After 13 hours of suspension in a fine-mesh strainer (refrigerated, of course) and some manual compression, about a tablespoon of water came out of my ricotta. Perhaps the ricotta’s wetness varies by brand.
Strain the ricotta as long as desired and mix in the powdered sugar.
Don’t refrigerate the Nutella. Seriously, just don’t.
The chocolate gets used twice: as chips for the ricotta mixture and as a layer between the nutella and canolli. The Lindt bars were slightly too thick for both purposes, so I remelted it into a thinner sheet.
Melt the chocolate with a double broiler, then pour into a large (9-in by 13-in or so) metal baking pan (the chocolate won’t cover the whole dish). Let cool in refrigerator until hard, 45 min. Peel the chocolate sheets off with a spatula (this might have been easier with parchment paper). Make about 2c of 1-cm chips, then cut the rest into 1-inch squares. Mix the chips into the ricotta. Set aside the squares.
Spread the nutella (gently) into the cooled crust. Arrange chocolate squares in some cool pattern that won’t be visible in the final dish, and press firmly into nutella.
Spread ricotta liberally over chocolate layer, with more in the center. Sprinkle powdered sugar on top. Serve. The pie can be refrigerated, but the nutella will harden and be less flavorful after an hour or two chilled.