Mix together the flour, salt, and baking powder., Work in the cold butter until the mixture resembles wet sand., Add the milk and stir until dough becomes cohesive., Turn the dough out of the bowl onto a clean surface, and knead until it becomes smooth, about 1 minute., Divide the dough in half, shape each half into a rectangle and wrap them in plastic. Set the pieces aside to rest for 30 minutes., Preheat the oven to 375°F., Roll one piece of dough out on a lightly floured work surface as thinly as possible, 1/16" or thinner, or roughly 16" x 8" to 10"; rolling the dough on a piece of parchment paper is very helpful here., Cut the dough into 1" to 2" squares and place them on a parchment-lined baking sheet; if you've rolled the dough out on parchment, simply transfer the parchment to the baking sheet., Lightly brush the crackers with olive oil and sprinkle them with salt, then bake them for 12 to 15 minutes, until crisp and lightly golden.