Preheat your oven to 325°F. Grease well a standard loaf pan (about 9-inches x 5-inches, or a bit smaller) and set it aside.

In the bowl of a stand mixer fitted with the paddle attachment or a large bowl with a handheld mixer, cream the butter on medium-high speed until it is light and fluffy.

Add the sugar, and then the eggs (slowly, while the mixer is on low speed) and vanilla, beating after each addition until well-combined. Turn the mixer speed up to medium-high, and beat until smooth.

In a small bowl, place the flour blend, xanthan gum and salt, and whisk to combine well. Add the flour mixture, about ¼ cup at a time, to the mixer bowl with the wet ingredients, and mix until just combined.

The batter will be thick but soft and smooth. Scrape the mixture into the prepared loaf pan, and smooth the top with a wet spatula. Carefully bang the bottom of the pan a few times on the counter to release any air bubbles.

Place the loaf pan in the center of the preheated oven and bake, rotating once during baking, until lightly golden brown all over and a toothpick inserted in the center comes out clean (about 50 minutes).

Remove from the oven and place the cake, still in the pan, on a wire rack to cool for at least 30 minutes before removing from the pan and allowing to cool completely.