Clip a candy thermometer onto the side of a 4-quart Dutch oven; add oil to pan. Heat oil to 385°.
While oil heats, weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, paprika, baking soda, and black pepper in a medium bowl. Gradually add club soda, stirring with a whisk until smooth.
Dip beans, 1 at a time, in batter, coating completely. Add to hot oil in a single layer. (Do not crowd pan.) Fry, in batches, 1 minute or until golden, turning once. (Maintain temperature of oil at 375°.) Drain beans on a paper towel–lined jelly-roll pan. Place pan in oven, and keep warm at 200° until ready to serve. Sprinkle beans evenly with salt just before serving. Serve with Mild Cayenne Sour Cream.
When frying, choose a healthy oil that has a high smoke point and is low in saturated fat, such as peanut, soybean, or canola oil. Then place it in a deep skillet or Dutch oven. The pan you choose should depend on the food you'll cook—you don't want to overcrowd the pan. Clip a candy thermometer to the side of the pan, and then watch the temperature very closely. If the oil is not hot enough, the food will soak up extra oil.