I went through two whole batches of rock-hard biscotti before I caved and got one of those... my oven was running almost 40 degrees cold. I felt so dumb, all that time I was just cranking the timer up thinking I was the problem.
Oh man, that's the worst kind of kitchen mystery. I did the same thing with cookies for months, just kept pulling out these sad, pale puddles thinking my recipe was cursed. Turns out my oven was basically just a warm box with a light. Felt like a total genius when the first batch actually browned after the fix.