I admit that I haven’t! However, I think you’re talking about baking in a crappy solar oven, not baking in a solar oven in general. For example,
http://www.solare-bruecke.org/infoartikel/Papers_%20from_SCI... describes a 3.4m² kilowatt prototype solar oven successfully used to cremate chunks of goat meat at temperatures of 800° to 900° in under an hour.
Larger solar ovens (usually known as “solar furnaces”) can reach 4000°, adequate not just for cooking or even cremation but also for firing terra-cotta, blowing glass, calcining lime, firing earthenware, making glass, firing porcelain, calcining portland cement, making borosilicate glass, casting aluminum, melting porcelain, purifying metals by zone melting, casting iron, smelting iron, casting steel, melting lime refractory, making quartz glass, casting basalt, boiling aluminum, vaporizing steel, vaporizing quartz, vaporizing lime refractory, melting tungsten, and sublimating graphite. Although people have been doing most of these with solar ovens for a while, especially the famous solar furnace at Odeillo, you can’t do all of these with Iron Age materials; apparently if you want to do anything useful with melted tungsten, you have to use Ta₄HfC₅ or similar.
Of course none of this works when it’s cloudy or dark, although molten-salt heat storage might be a usable solution to that even at a household scale.