Preheat the oven to 180C/350 and line a loaf tin with parchment paper. Melt the butter. To a large mixing bowl, add the almond flour, whey isolate, xanthan gum, salt, and baking powder. Whisk to combine. Ensure that the mixture has no lumps.
In another small bowl, add the melted butter, powdered erythritol, and almond milk. Whisk until the erythritol is fully dissolved and a mixture with a uniform consistency is formed. Pour the wet mixture into the bowl with the dry ingredients. Gently mix using a spatula to incorporate fully. The mixture will look lumpy, but that is okay.
Then, add in the water and gently mix using a spatula until a thick batter is formed. The thickness of the mixture should be slightly thicker than that of regular cake.
Pour the mixture into the loaf tin lined with parchment paper. Add the jam and swirl using a toothpick or the edge of a small knife. Transfer the bread batter to the oven and bake for 30-35 minutes until a toothpick inserted in the middle of the bread comes out clean and the top of the bread is lightly golden.
Allow the bread to cool in the loaf tin before removing it. Cut the bread into ½ inch thick slices and enjoy it with family and friends. Serve with butter, more jam, and a warm cup of coffee or tea.