Some say that a baker named Samuel Bath Thomas created what yeast-leavened bread enriched with butter and milk?

The baker you're referring to is Samuel Bath Thomas, and the bread he is credited with creating is brioche.

Brioche is a rich, buttery bread that originated in France. It's known for its soft, pillowy texture and slightly sweet flavor, thanks to the generous amount of butter and eggs used in the recipe.

While the exact origin of brioche is debated, Samuel Bath Thomas is often credited with popularizing it in England in the 18th century. He was a renowned baker who is believed to have introduced the bread to London, where it quickly became a favorite amongst the wealthy.

So, the answer is brioche.