Pastry: Put dry ingredients directly into a 9 or 10 inch pan. Combine oil and milk in measuring cup, beat with a fork until creamy. Pour all at once over dry ingredients, mix with fork until flour is completely dampened. Push dough with fingers to line bottom and sides of pie pan. Fluted works best. Pie: Spread rhubarb over pastry. Mix brown sugar, flour, salt, and cinnamon. Work in the melted butter. In another bowl, beat the eggs, add milk and vanilla. Gradually blend in the dry ingredients. Pour the mixture over the rhubarb in the pie shell, being sure all is coated. Sprinkle with blended topping. Bake 350 degrees for 1 and a half hours, until custard is set Topping: Mix softened butter with brown sugar and flour until crumbly and spring over pie before cooking.