In a medium-sized saucepan, heat the oil and sauté the shallot over high heat until browned, about 3 minutes. Add the wine and bring to a medium boil, then add the thyme and rosemary. Reduce by one-third, adding the stock and tomatoes. Continue to reduce for 5 - 7 minutes more and remove from heat.
Strain the mixture into separate bowls, reserving the tomatoes, shallots, and herbs in the strainer. Return the liquid to the saucepan and bring to boil. Thicken the sauce with the cornstarch and water, then stir in the reserved tomato mixture.
Keep warm.
In a large, hot cast-iron skillet, melt the butter and cook the steaks, searing both sides and turning often, until the steaks are done (usually rare to medium), about 7 - 10 minutes.
Place the tournedos on serving plates and pour the sauce over each. Serve immediately.