Lasagne: the dish we all love to eat, but not to make. Seductive slippery sheets of pasta, basted with rich ragu, sliding under creamy white sauce and a golden, bubbly top – sounds good. But spending four hours making a slow-cooked ragu, tenderly cooking out a béchamel and playing lasagne-sheet Tetris? This is the sort of thing that weekend cooking enthusiasts love, weeknight supper providers not so much.