Gold Laced x Mottled
Cross the f1 together
Hatch as many as possible 100 plus would be ideal and if your lucky one or two will be gold laced mottled.
Cross these Gold Laced Mottled back over Gold laced or if you get a pair you can cross them together.
Cross the f1 of Gold LacedxTolbunt and some should be both gold laced and mottled with much better lacing.
If you were working with Wyandotte then I would use a Mottled Orpington (for size), all the other mottled large fowl I can think of are Mediterranean and it will be harder to get back the Wyandotte type. A large fowl mottled cochin could work also, feathered legs are surprisingly easy to breed out. There will be a whole lot of culls and this will take a number of years. There could be some interesting new colors that pop out though.