1. Roll out the pie crust in a tart pan and prick the bottom with a fork. Chill in the refrigerator.
2. Peel, deseed and cut the butternut squash into cubes.
3. Preheat the oven to 180 degrees Celsius (350 degrees Fahrenheit).
4. In a pan, heat the oil and add the butternut squash cubes. Cook them over medium heat for about 15 minutes, until they are tender.
5. Meanwhile, in a bowl, beat the eggs and the heavy cream. Season with a little salt and pepper. Cut the feta into small cubes.
6. When the butternut squash cubes are tender, season with salt, pepper, and add a pinch of nutmeg (optional). Add the spinach leaves to the pan and sauté for 2-3 minutes until they wilt slightly. Remove from heat.
7. Spread the butternut squash and spinach on the bottom of the tart. Sprinkle the feta cubes on top. Pour the egg-cream mixture over the vegetables and feta.
8. Bake the tart for about 30 minutes, until the mixture is set. A few minutes before the end of cooking, add the sliced almonds on top of the tart.