Add the olive oil to a heavy, medium sized saucepan over medium heat, add in the shallot and saute for 2 minutes, add in the garlic, thyme sprigs, and salt & pepper, saute for 2 more minutes. Add in the balsamic vinegar and let it cook off, about 3-4 minutes. Add in the red wine and the beef stock, bring to a boil, then reduce the heat and let it simmer for 25 - 30 minutes or until reduced by ⅔. Strain the sauce into a clean saucepan and add in the butter, stir to melt. Taste and add salt if needed. Add the butter and olive oil to a heavy skillet, cast iron if you have one, heat almost to the smoking point, season the filets with a little salt & pepper and cook 3 minutes on each side. Using tongs, brown the edges of the filets also.To serve, spoon some of the reduction sauce on a serving plate, top with the filet, and another pat of butter if desired.