Place a steamer basket in a wide pan, fill with water until it is just below the bottom of the basket. Add the squash, season with salt, cover and cook over a medium heat for approx. 25 mins. until soft. Puree the squash, cool slightly.
Mix the squash, ricotta, sage, lemon zest and lemon juice, season.
Halve each piece of pasta dough lengthwise, divide the mixture into four. Place 10 portions on the bottom halves of the 4 pasta strips at equal intervals. Brush the upper halves of the pasta strips with a little egg, fold over the filling, press the edges down firmly, pressing out any trapped air. Separate the ravioli using a pastry wheel, transfer to a tray lined with baking paper. Brush the ravioli with butter.
Approx. 10 mins. in the centre of an oven preheated to 220°C.
Mix the yoghurt and herbs, season. Serve as a dip with the ravioli.