1. In a saucepan, pour in a carton of heavy cream with the chicken bouillon cube.
2. Once dissolved, add the frozen spinach and the second carton of cream, cover, melt over low heat (about 6-7 minutes), and stir regularly.
3. The mixture should be smooth; if it is too thick, add a little milk.
4. In a suitable rectangular dish (approximately 20 cm-25 cm), pour a first spoonful of sauce on the bottom of the dish so that the first layer of lasagna does not stick.
5. Then, build the layers of lasagna by alternating layers of spinach with Gruyère or Parmesan cheese.
6. On the last layer, finish with Gruyère and Parmesan cheese, as well as a thin layer of breadcrumbs.
7. The whole dish should be bathed in cream but will be absorbed by the layers of lasagna.
8. Bake at 200°C (392°F) for 30 minutes.