A rectangular form of cheese.
As Mrs.B says "Brickbat cheese has nothing remarkable except its form. It is made by turning with rennet a mixture of cream and new milk. The curd is put into a wooden vessel the shape of a brick, and is then pressed and dried in the usual way."
The 1880 'American encyclopædia of commerce' has; "Brickbat Cheese, an English cheese made in Wiltshire of new milk and cream, so named from the shape of the square pieces into which it is formed."