In a food processor combine the cookies and sugar and pulse until fine crumbs form then pour in the butter and pulse until crumbs are just coated. (foodsofourlives.com)
You could also place topping ingredients into a small food processor and pulse until coarse crumbs form. (mostlyhomemademom.com)
Pour in butter and stir until large crumbs form. (doughseedough.net)