Add the tomato juice into a large or high-sided saucepan, bringing it to a high-simmer over medium-low heat.
Slowly add the baking soda, whisking in a little to a time, constantly stirring as you do it.
When the foam settles with constant stirring, add the butter, continuing to stir until melted. 
Add the milk and a dash of salt and pepper, continue to simmer until ready to serve.
Footnotes: Tomato juice naturally is acidic, so when adding the baking soda, it foams up in the pan. Note, take care to use a high-sided pan to keep up with the foam rising, and add the baking soda slowly, constantly stirring as you do it.