- In a shallow 2 quart baking dish, mix 1 ¼ cups sugar and tapioca.
- Add rhubarb, raspberries, and lemon juice; mix gently but thoroughly.
- Let stand 15 minutes to 1 hour to soften tapioca; mix several times.
- Meanwhile, in a food processor or a bowl, whirl or rub together with your fingers the matzo meal, the remaining ½ cup sugar, margarine, and nutmeg until fine crumbs form.
- Squeeze to compact into lumps, then crumble over rhubarb mixture.
- Bake in a 375 °F.
- Oven until cobbler is bubbling in center and top is golden brown, about 1 hour.
- Let cool 15 minutes; spoon cobbler into bowls and top with sorbet, if desired.