Combine flour, salt, sugar, and baking powder in a medium bowl.
Add your cold butter and cut into the dough until a sandy mixture forms.
Add your cold water and work into a dough. Do not over-mix.
Split your dough into 3 bowls. In one, add your squid ink. In another, add matcha. Keep the first dough plain.
Press all three doughs together until you have a marbled, striated oyster shell-like dough.
Preheat oven to 375°F.
Roll into a thin dough on a floured work surface, about 1/8” thick.
Cut dough into teardrop shapes and form aluminum foil shell molds by crunching and shaping small squares of tin foil.
Spray each tin foil mold lightly and place a piece of cracker dough on top. Shape around the tin foil but leave the bottom uncovered to keep dough from trapping the tinfoil.
Arrange shells on a parchment-lined baking sheet and bake for 12-15 minutes until lightly browned and crisp.
Let cool for a few minutes and remove tinfoil molds. Serve as a snack or on top of soups and chowders.