Zest and juice lemons, separately, reserving zest and juice; set aside.
Melt ¼ stick of butter in microwave.
Generously coat each fillet with salt and pepper; then brush with melted butter.
Add seasoned fillets, presentation side down, to a very hot cast-iron skillet, and sear to get a nice crust, 2 to 3 minutes. Carefully turn and sear other side, about 3 minutes. Remove from heat, and set aside.
Melt remaining 2 sticks of butter in a large saucepan over medium-high heat. Allow butter to foam and turn golden brown. Watch carefully, and lower heat if necessary. Do not allow butter to burn, or it will be unusable. Immediately add lemon juice, salt and pepper.
Remove from heat, and add crawfish tails and parsley.
Plate fillets, and drizzle with crawfish tails and browned butter.
Sprinkle with lemon zest, and serve.