Trim excess fat from beef. Put cubed beef in a bowl and toss with salt and pepper. Heat 3 tablespoons oil in Dutch oven over high heat. Add half the cubed meat and sear until browned on all sides; remove with slotted spoon and place in a separate bowl. Add rest of oil to Dutch oven and repeat steps with second batch of meat.
Turn heat down to medium; add shallots to pan and cook until golden. Add flour and cook 3 minutes, then add Guinness, stock, tomato paste, and brown sugar. Cook 1 minute, then return meat to pan along with carrots and porcini mushrooms. Bring to a boil, then turn heat down to medium low and cover. Simmer, stirring occasionally, 45 minutes.
Stir in portobello mushrooms, thyme, and peas; cook 5 minutes. Taste and adjust seasoning as needed. Pour into baking dish and let cool in refrigerator. When filling has cooled slightly, roll out crust. Lay crust over filling, folding edges over as needed. Brush crust generously with egg wash, cut steam vents, and bake 35 to 40 minutes, until crust is golden brown.