i'd just throw it all into a bowl, melt the butter in a jug and mix the butter into the dry with a knife
My crumble is never the same twice tbh...I use a combination of flour, oats, muesli, butter, sugar (sometime brown, or golden, or caster, or demerara) biscuit crumbs, flaked almonds, chopped/crushed nuts, ground almonds....plus a shake of random spices to match the fruit.
It's a thorough rake about the cupboard to use up odd ends of things...esp all the fancy flours I buy.
I tend to overmake quantities too, so have often got random bags of crumble mix, and cheesecake biscuit base crumbs in the freezer, so i haul them all out and use them up!!
My best one ever was a Chocolate Pear crumble...pears in the bottom, they were very ripe so no precooking required, a squoosh of pear liqueur that had been hanging about, some sugar and then a collection of crumble bags from the freezer, plus some bashed chocolate digestive crumbs, choc chips and a good couple of tbs of cocoa in the crumble mix.