Preheat your oven to 375°F. Grease a 9-inch round baking pan or a 10-inch cast iron skillet, and set it aside.

In a large bowl, place the flour, xanthan gum, baking powder, baking soda, salt, cream of tartar, and granulated sugar, and whisk to combine well.

Add the chopped and chilled butter, and toss to coat the butter in the dry ingredients. Between your well-floured thumb and forefinger, flatten each chunk of butter and return it to the dry ingredients.

Add the raisins (more or less, to taste), and toss to coat the raisins in the dry ingredients.

Place 1 1/2 cups of the chilled buttermilk in a large measuring cup or bowl with a pour spout, add the eggs, and whisk to combine well.

Create a well in the center of the dry ingredients, add the buttermilk and egg mixture and mix gently to combine. The dough should come together.

With clean hands, knead the dough gently. If there are any spots that are dry and crumbly, add more buttermilk sparingly by the tablespoon as necessary to bring the dough together.

Turn the dough out onto a lightly floured surface and sprinkle lightly with more flour. Pat the dough into a round that is approximately 9-inches in diameter, piling it higher toward the center and sprinkling lightly with more flour as necessary to prevent sticking.

Place the dough in the prepared baking pan and, with a very sharp knife, slice a large “X” on the top about 1-inch deep (each slash should be about 6-inches long). If the dough seems to have warmed during handling, place the pan in the freezer to chill for 10 minutes or until the butter is once again firm.

Place the baking pan in the center of the preheated oven and bake until a toothpick inserted in the center comes out clean and the bread is firm to the touch (about 45 minutes, depending on size).

Remove from the oven and allow to cool in the baking pan for 10 minutes before turning out onto a wire rack to cool further.

Slice and serve warm, with butter. It is also excellent the next day, toasted.