This is an imperial strength take on an uncommon, traditional British style. The name comes from my oldest daughter who once claimed her dirty diaper was "too brown" when she was just 2 or 3 years old and then continued to use that term whenever she wanted to avoid something. In this case, the beer is not to be avoided, but the term has continued to entertain my wife and I for years and it seemed like a good fit for an extra strength brown ale.
Most of us are familiar with the standard British Brown Ale, with Newcastle being a common introduction to it in the US, or hoppier American Brown Ale variations. Too Brown Ale is a sweet, extra strength version of a London Brown Ale, which is a much less common variation which is different enough that BJCP decided it needs its own category. A traditional London Brown Ale is much sweeter than the styles we are usually familiar with and relatively low alcohol.
I have chosen to classify this as a British Strong Ale for now because that is the closest match. Everything fits except the color and it seems to fit the intent. The only option which completely fit as far as technical specifications is Experimental Beer because anything goes there, but I don't feel that it quite matches the intent of that category. Another option would be Mixed Style Beer, calling it a mix of British Strong Ale and London Brown Ale.
This experiment is based on the Nutty Mann Brown Ale recipe from the book "Brewing Classic Styles" by Jamil Zainashef and John Palmer. It takes things well above London Brown Ale levels with an approximately 8% ABV, some additional caramel malts to go with it, and some additional hops to help balance that extra sweetness and keep the overall balance similar to its base. One of the challenges here is that a London Brown Ale can be seen as a small sweet stout. Making it bigger can easily just turn it into a Sweet Stout rather than just an extra strong London Brown Ale, although this even goes beyond that in terms of ABV and original gravity.