Wipe the mushroom with a damp paper towel to clean.
Remove the stems and then cut the smaller ones in half and the larger ones into quarters.
In a large bowl, whisk together the flour, Cajun seasoning, beer, and egg. *Note - the mixture should be the consistency of pancake batter.
Meanwhile, in a large, high sided pot bring approximately 2"-3" of oil to a temperature of 375°
Place approximately 10-15 mushrooms into the batter and use a spoon to carefully stir them to coat.
Use a set of tongs to remove the mushrooms, one at a time from the batter, and carefully add them to the hot oil.
*Note - If you add the mushrooms all in at once to the hot oil they'll stick together, which is why it's best to add them individually.
Fry the mushrooms, stirring carefully and occasionally for approximately 3-4 minutes or until they're golden brown in color.
Use a large slotted spoon to remove the fried mushrooms to a paper towel-lined bowl and season immediately with a light sprinkling of salt and pepper.
Continue the same process with the remaining mushrooms.
Prepare the sauce by whisking all the ingredients together in a small bowl.
Serve the mushrooms with the sauce and enjoy!