Cut the florets off the broccoli stalks; trim into 1/2-inch pieces. Cut the stems into 1/4-inch pieces. Peel the big stalks with a vegetable peeler; chop into 1/4-inch cubes.
Using a food processor, grind the bread into coarse crumbs. In a large skillet, preferably cast-iron, melt 2 tbsp. butter over medium heat until it sizzles. Add the breadcrumbs and cook, stirring occasionally, until golden, about 2 minutes. Transfer to a bowl. In the same skillet, cook the remaining 3 tbsp. butter, the onion and 1/2 tsp. each salt and pepper over medium heat, stirring, until nearly tender, about 5 minutes. Add the broccoli and 1/3 cup water and simmer, stirring occasionally, until crisp-tender, about 5 minutes. Toss with the breadcrumbs; let cool. Wipe out the skillet; reserve.
Halve the tenderloin crosswise into 2 pieces. Cut off the piece of meat from the thicker half; cut a lengthwise slit into it, slicing about halfway through to the work surface. Set aside.
Slice the thicker tenderloin half lengthwise down the center, cutting two-thirds of the way through to the work surface; open the meat like a book. Cut 2 more slits in the 2 sides of the book, slicing about halfway through (you will have 4 attached segments). Repeat this process with the remaining tenderloin half.
Pat the 3 tenderloin pieces dry and brush all over with EVOO; season with salt and pepper. Heat the reserved skillet over high heat. Add 1 tenderloin piece, uncut side down, and sear for 2 minutes. Flip; sear on the other side for 1 minute. Transfer to a cutting board and let cool while you repeat with the remaining 2 tenderloin pieces.
Preheat the oven to 425 degrees . Arrange five 18-inch-long pieces of string crosswise 1 1/2 inches apart on a work surface. Lay the thicker tenderloin half, cut side up, on top of the string. Spread half of the broccoli stuffing on the beef. Roll up and tie into a roast. Repeat with more string and the remaining tenderloin half, this time placing the reserved small filet piece next to the narrow end of the meat. Spread the remaining stuffing on top and tie up into a roast.
Place the roasts side by side on a large rimmed baking sheet. Roast until the internal temperature registers 125 degrees to 130 degrees , 25 minutes. Remove from the oven, tent with foil and let rest for 15 minutes. To carve, trim off a thin slice from the end, then cut each roast into 5 portions. Serve with the Blenderific Hollandaise.