Mushrooms release significant moisture that can make Yorkshire pudding bottoms soggy if not properly managed. Dice mushrooms finely for faster moisture evaporation and better distribution in small puddings. Cook over medium-high heat without crowding to encourage browning rather than steaming. The mushrooms should be golden brown and most liquid evaporated before seasoning - salt added too early draws out more moisture. Cool the mushroom mixture completely before assembly to prevent steam from softening crispy puddings. Properly prepared mushrooms add umami depth while maintaining pudding integrity. The concentrated mushroom flavor mimics the duxelles component of traditional Beef Wellington.