Prepare for Baking: Preheat your oven to 400°F / 200°C.
Line a baking sheet with parchment paper.
Pat the tenderloin steaks dry with a paper towel and season them generously on all sides with salt and pepper.
Sear the Tenderloin: Melt the butter in a heavy-bottomed skillet over medium-high heat.
Once shimmering, carefully place the steaks in the pan and sear for 2-3 minutes per side, until a deep golden-brown crust forms.
Remove the steaks from the skillet and set them on a wire rack to cool completely.
Create the Fathead Pastry: In a microwave-safe bowl, melt the shredded mozzarella cheese for 60-90 seconds, until fully melted and bubbly. Immediately add the almond flour and stir vigorously with a spatula until a smooth, uniform dough comes together.
Roll Out the Dough: Place the warm dough between two sheets of parchment paper.
Using a rolling pin, roll it out into a large rectangle, about 1/8-inch thick.
Remove the top layer of parchment and cut the dough into four equal squares.
Assemble the Wellingtons: Spread a thin, even layer of liver pâté (about 0. 5 oz / 14 g) onto the center of each dough square.
Place one cooled, seared steak on top of the pâté.
Wrap and Seal: Gently fold the sides of the dough up and over each steak, trimming any excess. Pinch the seams together firmly to create a complete seal.
Place the wrapped Wellingtons seam-side down on the prepared baking sheet.
Bake to Perfection: Bake for 25-30 minutes, or until the pastry is a deep golden brown and cooked through.
Let the Wellingtons rest for 5-10 minutes before serving to allow the juices to redistribute.
Work with the fathead dough while it's still warm. If it becomes stiff and hard to roll, microwave it for 10-15 seconds to make it pliable again.