Start with making roux. In a skillet, heat 1 Tablespoon unsalted butter over medium-high heat. Add 1 Tablespoon all-purpose flour and stir until combined and begins to bubble. This should take about 3-4 minutes.
Add 1 cup plum butter and ½ cup beef broth. Stir and season with ¼ teaspoon ground cinnamon, and 1 teaspoon lemon zest, and ½ teaspoon salt. Reduce heat and simmer gently for about 10 minutes.
Finally, add 1 Tablespoon spiced rum and stir. If the sauce is too thick, add a little more broth. Taste and adjust seasoning with salt and sugar if needed.
Notes
The basic recipe makes 4 portions.
SERVING: To serve, pour a small ladleful onto the plate and spread it out. Place a slice of warm meat on top of the sauce. For a side dish, preferably add Czech bread dumplings.
Put any remaining sauce in a sealable container and store it in the refrigerator. It will last for about five days here.
Reheating: Heat the sauce in a small saucepan on the stove. If the sauce is too thick, stir in one to two tablespoons of water.