The Gentleman's Beef Wellington

1-1/2 lbs. beef tenderloin, as uniform thickness as you can find
1-1/2 cups button mushrooms, chopped
1/2 cup frozen spinach, drained and chopped
1 medium onion, chopped
1 package of frozen puff pastry, thawed
2 Tablespoons J. Brady's The Gentleman's Shake, divided
2 Tablespoons Canola, Avocado or Olive Oil
1 egg beaten
Preheat the oven to 425 degrees.
Season tenderloin with one tablespoon Gentleman's Shake. Heat oil in a skillet on medium-high heat, 2-3 minutes per side to brown and remove. In the same skillet saute mushrooms, onions, spinach and the remaining tablespoon of J Brady's Gentleman's Shake for 6-8 minutes, let cool.
Roll out puff pastry on lightly floured surface. Cut pastry in half  Spread half mushroom mixture over one puff pastry half. Lay the seared tenderloin over the mushroom mix. Cover the tenderloin with remaining mushroom mix and other sheet of puff pastry.
Crimp the edges of the puff pastry all around to seal. Make a few thin slits in the top of the pastry. Brush the pastry All over with beaten egg. Bake the Beef Wellington in a 425 degree oven for 45-50 minutes or until pastry is deep golden brown and meat reads at least 125 degrees on meat thermometer. Allow to rest for 15 minutes. Slice into thick slices and serve!