one block of tofu
Counter 一丁 is used for blocks of tofu, as well as for other block-shaped foods and items.
I bought one block of tofu at the supermarket.
一丁 is a counter for blocks or pieces; 豆腐一丁 specifically means one block of tofu.
Compound of 豆腐 (tofu) and 一丁 (one block). The counter 丁 is used for blocks of tofu and other block-shaped items.