Preheat your oven to 350°F (180°C) and grease a deep pie dish or baking dish with butter.
In a large mixing bowl, toss 1½ lbs strawberries with ¼ cup superfine sugar, ¼ cup almond meal, 2 Tablespoons Pimm's No. 3 Cup, 1 Tablespoon minute tapioca, 1 Tablespoon cornstarch, and ¼ teaspoon salt. See notes by each ingredient for substitutes.
Pour the filling into the buttered dish and spread it along the bottom of the dish evenly.
Mix together ⅔ cup instant oatmeal, 1 teaspoon baking powder, ½ cup slivered almonds, ½ cup demerara sugar, and 5 Tablespoons butter in a bowl until combined.
Use a pastry cutter, fork, or a food processor to cut or pulse the cold butter into the dry ingredients until just combined. Do not over process into a paste!
Sprinkle the crumble on top of the filling in the baking dish. Bake in the preheated oven for 40-45 minutes for fresh strawberries or 50-55 minutes if you are using frozen.
Start checking for bubbling filling about 30-40 minutes in. Once it is bubbling, bake for about 10 minutes more. You need the filling to boil and bubble to help activate the tapioca and cornstarch so it will thicken up.
Remove from the oven and allow to cool for about 10 minutes before serving with heavy cream if desired. If you are baking this a day or two before you are serving, cool the crumble completely, cover it with cling film and refrigerate. You can serve the crumble warmed in the microwave or oven, but I must say that some folks love it cold!