Heat the milk in a saucepan and add the sugar, stirring until the sugar dissolves. Allow to cool until tepid.
Butter or line a large baking sheet (or two).
In a large bowl, combine the flour, baking powder, sweet clover, cream of tartar, and salt. Grate in the cold butter, toss with the flour, and rub between your fingertips until it resembles small crumbs. Pour the milk into the dry ingredients and mix well but briefly (overworking will make the rusks tough).
When it is mixed, use your dominant hand (or a spoon) to remove chunks from the soft dough (approx. 4 inches x 2 ½ inches, or about 3¼ oz weight, for biscuit-sized rusks). Shape gently and briefly into casual oblong shapes. Jagged edges are fine. Place them in rows on the baking sheet with about a half-inch between them.
Bake for about 20 - 23 minutes. They should not be brown - more blonde. Remove and while still warm gently break each rusk apart using forks, or slice gently apart with a bread knife. When the oven is cooler dry them completely for about 6 hours at 200'F or lower. They are ready when they are shatteringly dry.