In a medium bowl, whisk together the flour and salt.
In a separate bowl, beat the eggs and then whisk in the milk and 2 tablespoons of vegetable oil.
Gradually add the wet ingredients to the dry ingredients, whisking until just combined. Do not overmix.
Lightly grease a mini muffin tin with vegetable oil.
Pour about 1 tablespoon of batter into each muffin cup.
Bake for 15-20 minutes, or until the Yorkshire puddings are puffed and golden brown.
While the puddings are baking, prepare the beef filling. In a small bowl, combine the mayonnaise, Dijon mustard, and Worcestershire sauce. Season with salt and pepper.
Gently stir in the thinly sliced roast beef until evenly coated.
Once the Yorkshire puddings are out of the oven and slightly cooled, carefully remove them from the muffin tin.
Spoon a small amount of the beef mixture into each Yorkshire pudding cup.
Garnish with chopped chives or a dollop of horseradish cream, if desired.
Serve immediately.
Notes
Ensure your oven and oil are hot before pouring the batter for the best puff.