Preheat oven to 375F.
To prepare crumble, combine flour and sugars in a large bowl. Cut in butter with two knives or your fingers until crumbly. Stir in walnuts.
To prepare filling, combine pears, cider, lemon juice and flour in a large bowl. Spoon into an 8-inch square baking dish. Dot with marmalade. Sprinkle with crumble mixture.
Bake 40 minutes or until fruit is bubbling at edges and top is golden brown.