Set a medium saucepan over medium heat and add the butter, brown sugar replacement, and allulose or BochaSweet. The mixture should melt together, then bubble steadily as the butter begins to brown and smell lightly nutty.

Let the mixture boil for 3 to 5 minutes, whisking as needed and watching the color closely. Look for small amber specks and a deeper golden tone, because allulose can go from perfect to scorched fast.

Take the pan off the heat and pour in the heavy cream gradually while whisking. The caramel will surge with aggressive steam and fast, loud bubbles before settling into a smoother foamy boil.

Sprinkle the xanthan gum over the surface in a light, even shower while whisking hard, then add the salt. If the xanthan goes in slowly, it disappears into the sauce instead of forming little gel clumps.

Return the saucepan to the heat and boil the sauce for 1 more minute. The bubbles should look tight and rapid, which shows the cream has fully integrated into the caramel base.

Cool the sauce to lukewarm, then stir in the water until the texture is smooth and evenly loosened. It will seem thin in the pan, but it thickens noticeably as it stands and even more once chilled.

For a salted caramel version, stir in the additional salt at the very end. The flavor should shift from mostly sweet to balanced and slightly deeper, without tasting flat or harsh.