I searched through the dulce de leche cookbook I have, Dulce de Leche: Recipes, Stories and Sweet Traditions (eG-friendly Amazon.com link), and it does not mention dulce de leche solido as an ingredient. Some of the recipes call for a thicker confectionary version, dulce de leche repostero, and there's a recipe for that but it's still a thick spread, not a solid like your photos.