Stock is already quite salty so be careful to not over salt the soup.
Slice the beef chuck into bite size cubes roughly 2cm x 2cm.
Heat a splash of olive oil in a large saucepan over a medium-high heat and brown the beef cubes in batches. By not overcrowding the pot, the meat will caramelize and retain its flavoursome juices.
Remove the beef from the saucepan and set aside to rest.
Reduce the heat to medium, add the butter and the onions and sauté until lightly browned. Stir in the garlic and cook for an additional minute.
Add half the mushrooms and simmer for about 5 minutes or until soft.
Pour in the beef and vegetable stock, stir well and bring to the boil.
Remove the pot from heat and allow to cool for a few minutes. In two batches, using a food processor or a blender, blend the mixture well.
Using the same saucepan, return this mixture to the heat and add the remaining sliced mushrooms, browned beef with its juices and thyme sprigs. Season to taste with salt and pepper.
Cover the saucepan and cook for 1 hour on a medium-low heat, stirring occasionally.
Stir in the cream along with a tablespoon of flour and bring to the boil. Lower the temperature to a medium heat and simmer for 10 minutes until thickened. Remove thyme sprigs and serve the soup hot with fresh crusty bread for dunking.