COMBINE flour, salt, mustard, paprika and pepper in large resealable plastic bag. Pour buttermilk in small bowl. Add mushrooms. Toss to coat. Place mushrooms in bag with flour mixture. Shake to coat.
HEAT 2 to 3 inches oil in deep-fryer or heavy saucepan to 375ºF. Fry a few mushrooms at a time 2 to 3 minutes, or until deep golden brown, turning over several times. Drain on paper towels. Serve hot with a dipping sauce, if desired.
Serving Size (1/4 of recipe), Calories 200 (Calories from Fat 130), Total Fat 15g (Saturated Fat 1.5g, Trans Fat 0g), Cholesterol 0mg, Sodium 330mg, Total Carbohydrate 15g (Dietary Fiber 1g, Sugars 3g), Protein 4g; Percent Daily Value*: Vitamin A 2%, Vitamin C 2%, Calcium 4%, Iron 6%.
*Percent Daily Values are based on a 2,000 calorie diet.