My friend told me about Landeau Chocolate when she and her family were visiting Lisbon in December 2021. I kept it in my mental databank for future reference.
I looked it up to find that there are three locations in LX Factory, Chiado and El Corte Ingles. The one in Chiado is located at Rua das Flores, 70. That's not far from where I'm staying so I put the address in Google maps and set off.
Rua das Flores, 70
Phone: +351 917 278 939
They are open everyday: 12:00 pm - 7:00 pm (except Christmas Day and New Years Day)