A buck ninety doesn’t buy much these days. But in the heart of Silicon Valley, where change happens in nanoseconds and the new and the novel are celebrated above all else, it will still get you a fresh, warm and sweet taste of joy, one that hasn’t changed in 66 years. Hand over two crisp Washingtons at Stan’s Donut Shop in Santa Clara, and you’ll receive back not only a dime, but an irresistible, pillowy, yeasted donut smothered in sugary glaze, its runaway best-seller.