Once drained, transfer the ricotta to a mixing bowl and set aside.
Heat the olive oil in a large frying pan over medium heat. Add the garlic and cook for 1 minute, then add the spinach. Season with salt to taste and cook until the spinach wilts. Transfer cooked spinach to the colander. Use the back of a ladle to push down on the spinach and squeeze out excess moisture. Allow to cool.
To make the spinach and ricotta filling, add the cooled spinach to the mixing bowl with ricotta. Add the 30g Parmigiano Reggiano (or Grana Padano), chopped sage and sea salt to taste. Mix with a spoon until well combined.
To make the lasagna rolls, place sheets of cling film on a work bench. You will need one cling film square for each sheet of pasta, noting that the cling film should be larger in size than each pasta sheet. Place a pasta sheet on top of each cling film square.
Spoon a thin layer of the spinach and ricotta filling evenly over one pasta sheet leaving a 1cm border on one of the long side edges (to create a seal). Scatter fontina cheese over the spinach and ricotta filling. Brush some water on the 1cm border, then roll up the pasta tightly to enclose the filling, starting with the filled side and ending with the water brushed border to create a seal. Wrap the lasagna roll tightly in cling film. Repeat with the remaining pasta sheets and spinach and ricotta filling, again wrapping tightly in cling film. Freeze the lasagna rolls for 1 hour to firm up.
Meanwhile, preheat the oven to 200°C conventional oven/ 180°C fan-forced (392° Fahrenheit/Gas 6).
To make the Besciamella (Bechamel) sauce, melt the butter in a medium-sized saucepan over medium heat until foaming. Add the flour and stir with a wooden spoon to form a smooth paste (a roux). Allow the flour and butter mixture to cook for a minute (but do not allow it to brown). Remove from the heat. Slowly pour the cold milk into the roux, stirring constantly, until the mixture is smooth. Add the bay leaf and return to medium heat. Cook, stirring with the wooden spoon until the Besciamella comes to the boil and thickens (approximately 10 minutes). Remove from heat. Season with salt to taste and stir in freshly grated nutmeg. Set aside to cool slightly.
Ladle 1/2 of the Besciamella sauce into a large baking dish.
Remove the lasagna rolls from the freezer. Remove and discard plastic wrap. Use a sharp knife to cut one of the rolls into 3 or 4, depending on the size so that each piece is 3.5 to 3 cm wide. Place the rolls onto the Besciamella sauce with the filling facing up. Repeat with remaining lasagna rolls.
Drizzle the lasagna rolls using the remaining Besciamella. Grate extra Parmigiano Reggiano on top of the Spinach and ricotta rolls. Bake for 25 minutes or until the pasta is cooked through. Serve immediately – buon appetito!