Whilst the fruit is cooking down, separate the oats into two piles and blitz one half in a nutribullet or coffee grinder to turn into powder. Transfer this into a bowl with the whole oats and the butter cut into small chunks. Mix and combine this by hand, until the mixture is nice and crumbly. Then add the rest of the sugar. and mix again. You may need a little more butter but always start with less and build up.