Sear the short ribs for 3-5 minutes per side until you have a nice brown crust. Set the short ribs aside then add carrots, shallots, celery and leek. Sauté for 2-3 minutes until golden brown
Add garlic, thyme, bay leaves, parsley ½ tsp salt and ¼ tsp pepper. Stir and let cook for about 1 minute then add the tomato paste and cook another 3 minutes. Add the short ribs back in.
Add in the red wine and simmer for 10 minutes. Add the beef stock and bring it back to a simmer. Cover the pot and transfer it to the oven for 2-3 hours until meat is very tender and falling off the bone
In a small sauce pot melt the butter over low heat and whisk in the flour. Whisk in the flour and cook over low heat for 3 minutes, whisking frequently
Whisk in the roux (butter and flour mixture) and let the sauce come to a low boil so it thickens