The phrase "crumbly mixture" refers to a texture of something that easily breaks apart into small pieces or crumbs when touched or squeezed. Full definition
Place all ingredients in a bowl and combine using a fork or pastry blender until a coarse crumbly mixture forms. (paleorunningmomma.com)
Make the dough: In a food processor with a steel blade put cornstarch, peanuts, cocoa powder, powdered sugar, salt and butter and blend until crumbly mixture is formed. (lilcookie.com)
Press crumbly mixture into a long rectangular tart pan. (aclassictwist.com)