1. Heat oven to 375 degrees. Line baking sheet with parchment paper.
2. Season beef liberally with salt and pepper.
3. In a large sauté pan over medium-high, heat oil. When oil is just smoking, add beef. Brown on all sides, 1 to 2 minutes a side. Once browned, remove beef and place on rack to rest.
4. Add garlic to hot pan and cook until lightly browned, about 20 seconds. Add mushrooms and onion; cook until soft and tender and all liquid had evaporated, 8 to 10 minutes. Season with salt and pepper and add 2 teaspoons of thyme.
5. Set aside ¼ cup of mushroom mixture. Transfer the rest to a food processor and pulse to chop into ¼-inch pieces. Transfer to a bowl and refrigerate for 5 minutes. Once slightly cooled, add spinach and egg whites and mix well.
6. In a medium bowl, stir pancake mix with just enough water, about 1/3 cup, to moisten and make a dough that holds together but is not sticky. On a lightly floured surface, roll dough to a thin rectangle that is 2 inches longer than the roast. Place beef on dough. Spoon mushroom mixture on top and sides of beef and pat down tightly. Fold dough up and over the top of beef and spinach and crimp seams together.
7. Place meat seam-side down on baking sheet. Cut a few slits in top to vent. Bake for 35 to 40 minutes, or until center registers 140 degrees. Remove from oven, cover with foil and let rest for 10 minutes.
8. Meanwhile, place 2 of the porcini chunks in a spice grinder and grind to a fine powder. Place mushroom powder, remaining whole porcini mushroom chunks and shredded jerky in a microwave-safe bowl with 2 cups of water. Microwave on high for about 2 minutes, or until the water is simmering. Let sit for 5 minutes and repeat.
9. Pour Madeira in a small saucepan over medium heat. Bring to a boil and boil for about 5 minutes, or until reduced by half. Pour the mushroom and beef broth through a strainer into the reduced Madeira while pushing on the jerky and mushrooms to extract as much liquid as possible.
10. Remove whole pieces of porcini mushrooms from the strainer and roughly chop them, then set aside. Discard jerky. Bring broth and Madeira mixture to a boil.
11. In a small bowl, combine arrowroot and 4 tablespoons cold water. Mix well, then add to simmering sauce. Cook and stir for 1 minute, or until sauce is just thickened. Add soy sauce, remaining ½ teaspoon of thyme leaves and the reserved chopped porcini and reserved ¼ cup of the mushroom and onion mixture. Season to taste with salt and pepper.
12. Slice roast into 8 even slices and arrange on a platter. Serve with sauce.
Go to full version of