In a large bowl, whisk together the gluten free all-purpose flour, tapioca starch, sugar, salt, baking powder, and cream of tartar.
Add the cold cubed butter and use your fingertips or a pastry blender to cut it into the flour until the mixture looks like coarse meal with some pea-sized butter pieces remaining. This step is key for creating that signature flaky, buttery texture.
Drizzle in the cold milk and stir with a fork until the dough just comes together. Knead it gently a few times in the bowl until smooth. Wrap the dough in plastic wrap and refrigerate for 20 minutes.
Preheat your oven to 350F and line two large baking sheets with parchment paper.
Roll the chilled dough out between two sheets of parchment paper to about 1/16 inch thickness. The thinner the better for that classic crispy crunch. Use a 1 1/2 inch round cookie cutter to cut out circles and place them on the prepared baking sheets.Gather the scraps, re-roll, and cut until all the dough is used.
Poke each round three times with a fork to create the signature Ritz pattern. Brush the tops lightly with melted butter and sprinkle with a tiny pinch of flaky sea salt.
Bake for 10 to 13 minutes, until the edges are golden brown and the tops are lightly golden. They should puff up just slightly.
Brush with one more light layer of melted butter immediately out of the oven. Let cool completely on the pan until perfectly crispy and snappy.