A breakfast cup is (according to google) slightly smaller than a contemporary 250ml cup measure, so maybe just use a regular measuring cup and scoop a little bit out before you pour the ingredient in.

Cream butter and sugar. Add egg and beat lightly.

Dissolve baking soda in milk and add gradually (continue mixing) along with flour.

Add vinegar, and quickly stir in fruit.

I assume now is when you’d add the essence or spices, too.

Bake in a greased, lined cake tin, in a good oven for 2 hours. Not a bad oven, mind.

Just who was Janet and why was she such a recipe instruction gatekeeper? Again - I would be guessing at oven temperature, try 180°C.