Combine flour, baking powder, and salt in a medium bowl. Add sour cream and buttermilk, and mix with your hands until a dough forms. Turn onto a lightly floured surface, and knead for 5 minutes. Cover with plastic wrap, and let rest for 30 minutes.
Cut dough into 4 equal pieces. Using a lightly floured rolling pin, roll each piece into 8-inch rounds, less than 1/8 inch thick. Place tortillas on a parchment-lined baking sheet, layering parchment between each to prevent sticking. Cover with parchment, then with a damp kitchen towel. Let rest for 30 minutes (or cover and refrigerate overnight).
Place a cast-iron skillet over medium heat. Cook tortilla until brown spots appear, about 1 minute per side. Transfer to a plate, and cover with parchment and then a damp towel. Repeat. Serve immediately.
You can swap spelt flour for white or whole-wheat flour in almost any recipe. Expect a slightly more robust flavor than regular whole wheat provides.