Preheat oven to 375°F. Lightly grease a baking sheet with butter.
Put flour and sugar into a large bowl. Cut in the cubed butter with your hands, rubbing it into the flour/sugar mixture. Add the ginger and continue rubbing just until the mixture is starting to bind together.
Knead gently until you have a smooth dough that can be formed into a ball. (If dough is too dry to come together, add a bit more butter or a small squirt of lemon juice.)
Roll the dough into 8 to 10 smaller balls of equal size, depending on the size of the scallop shell you'll be using. (I used a large 4" scallop shell and got 8 large cookies).
Lightly dust the scallop shell with flour and sugar. Starting roughly in the lower middle, start pressing out a ball of dough against the shell to impress it, evening the thickness and shaping the edges as you go.
Carefully prise the cookie off the shell and place on a greased baking sheet, then repeat with the rest of the dough.
Bake at 375°F for 10-15 minutes, or just until a pale golden brown.