Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and prepare 9”x5” loaf pan (2lb/900g) with parchment.
In a bowl, sift together the gluten free 1:1 flour blend (w/xanthan), almond flour, baking powder, and salt. Set aside.
2 cup gluten free 1:1 flour blend, ⅔ cup almond flour, 3 teaspoon baking powder, ¼ teaspoon salt
Add the sugar and orange zest to a bowl and use your fingertips to rub the zest into the sugar. This helps to release more essential oils from the zest.
1 cup castor/superfine granulated sugar, 2 tbs zest of 3 oranges
Cream the butter and sugar (with the added orange zest) together until pale and fluffy. This can be done with a hand mixer or in the bowl of a stand mixer fitted with a paddle attachment.
¾ cup butter
Add the eggs, one at a time, mixing well after each addition, until well combined. It's very important that your eggs are at room temperature and that you add them one at a time to maintain the emulsion of the butter as much as possible. If you forgot to take your eggs out of the fridge, place them in warm tap water for 5-10 minutes before using them.
4 eggs
Add the vanilla and mix until combined.
1 teaspoon vanilla extract
Beginning and ending with the dry ingredients, alternately add the dry ingredients (in three batches) and the orange juice (in two batches) to the butter-sugar mixture, whisking well after each addition, until you get a fairly smooth cake batter with no flour clumps.
¾ cup orange juice
Transfer the cake batter into the prepared loaf tin, smooth out the top, and bake in the pre-heated oven at 350ºF (180ºC) for about 1 hour - 1 hour 5 minutes or until risen, golden brown on top and an inserted toothpick comes out clean. The loaf should have a large crack running along the center.
Allow to cool in the loaf pan for about 10-15 minutes, then transfer the cake out of the tin and onto a wire cooling to cool completely.