in the same frying pan over medium heat, melt the butter.
Add the shallot and parsley and saute until the shallot is softened, 2-3 minutes.
Remove the pan from heat and add the Cognac.
Briefly return to the heat to warm; then remove from the heat again to ignite the Cognac using a long kitchen match, making sure the overhead fan is off and averting your eyes. Keep a lid handly in case the flame should flare up.
When the flame has burned out, return the pan to high heat and whisk in the mustard, tomato paste, reserved 1 Tb rub, and beef stock.
Cook, whisking often, to reduce the sauce by half, 4-5 minutes.
Remove the pan from the heat and whisk in the cream and cayenne to taste.
Add any accumulated juices from the steaks. Season to taste with salt and black pepper.
To serve, spoon a generous amount of sauce over the steaks and serve at once. Pass any extra sauce at the table.