Split the bread lengthwise down the middle and lay cut-side up on a baking tray.
In a small pot, add the butter, paprika and garlic. Set over low heat and mix well until just melted, about 1 minute. In a mixing bowl, combine the mayonnaise with the cheeses, then pour in the melted butter and stir well. Season with the cayenne and salt.
Smear evenly over the bread, then bake until bubbly and golden brown, 10 to 12 minutes.
Sprinkle with Parmesan and parsley, then cut and serve.