Salt the venison well and let it rest at room temperature for 30 minutes.
Over medium heat, brown the venison on all sides in the butter. Using an instant read digital thermometer, cook the venison to your liking: 130-135° F for medium rare and 135-145° F for medium. Move the meat to a cutting board, tent loosely with foil and let it rest while the sauce is being prepared.
Using the same pan, ensure there is at least 1 Tablespoon of fat left in it -- add more if necessary. Sauté the shallot over medium-high heat for 90 seconds, just until soft. Take care not to burn the shallot.
Add the port wine and deglaze the skillet by scraping up any brown bits stuck to the pan. Bring to a boil and let reduce by half. Add the demi-glace (or stock), salt, citrus zest, mustard and cayenne and let boil for a minute or two. Stir in the Strawberry Smash and black pepper. Boil down until thick but still pourable.
Slice the venison into medallions. Pour any remaining juices from the meat into the sauce and stir to combine. Serve with the sauce over the meat or on the side.