spray the cooking crock with a non stick spray or lightly butter it

add the chopped berries and rhubarb-make sure you've figured out how sweet your berries are

sprinkle with the sugar and let them juice for 10 minutes, taste the berries are they sweet enough? they'll probably be too sweet but in this case they'll be carrying the rhubarb so too sweet is ok

if it's not sweet enough add more sugar and taste again

once the amount of sugar is figured out add the tapioca and stir to combine

turn cooker on to high and let it start warming up while you make the topping

mix the dry ingredients together in a mixing bowl or food processor

chop the butter into them until the mixture resembles dried crumbs, a couple of pulses with a food processor or a few minutes work with two knives or your hands

add the milk and the beaten egg and mix until just combined

drop by spoonfuls on the filling

cover the top of the crock with 3-4 layers of paper towels and then cover with the lid

cook on high for about 90 minutes but if you have an older cooker begin checking for doneness about 60-70 minutes in to the cook time

you're looking for a topping that's cooked all the way through so use a tooth pick to check it, if it's just got a few crumbs on it your topping is done

once the topping is cooked through remove the lid and paper towels, reduce cooking temperature to low and continue cooking for 30 minutes on low

it can be held on warm for another hour or so but I don't recommend covering it again you're topping will get soggy