Arrange pumpkin on a baking tray covered with parchment paper.
Drizzle a little olive oil over the top and add thyme sprigs and garlic.
Roast in a preheated oven to 360F/180F for about 30 min or until soft and cooked through.
Blanch spinach in a large pot of boiling water, then drain and transfer into a bowl with ice, to cool them down and preserve their bright green color.
Transfer into a bowl, add half the roasted pumpkin cubes and the rest of ingredients. Season with salt, pepper and a pinch of nutmeg.
Blend the remaining pumpkin to make a smooth puree and set aside.
Fold the cannelloni in a large pot of lightly salted boiling water. Cook for about 1-2 min, they should be still hard. Drain and pat dry on a kitchen cloth.
Fill a piping bag with the ricotta, pumpkin and spinach mixture.
Hold each cannelloni up on your palm to avoid the filling to escape and fill with the prepared mixture.
To make the white sauce: simply blend ricotta with a splash of milk/water until it reaches a creamy consistency. Adjust with more liquid if necessary. Season with salt, white pepper, sage and a pinch of nutmeg.
Layer the bottom of a small 9inch baking dish with half the pumpkin puree, and arrange cannelloni on top.
Pour over the remaining pumpkin puree and top with white sauce. Season with salt and pepper and bake in the oven to 360F/180F for 15-20 min, until the pasta is cooked through and the edges are slightly crispy.
Serve immediately and enjoy!