Preheat your oven to 180 degrees celsius.: As the oven warms you should notice a steady hum from the heating elements, and by the time the crumble hits the oven the interior will be evenly hot, encouraging even bubbling of the fruit. Preheating ensures the topping begins to crisp immediately, which prevents the fruit from overcooking before the crumbs brown. A common mistake is putting the dish into a cold oven, which yields a soggier topping. If your oven runs hot or cool, use an oven thermometer to confirm accuracy.
Grease an oven proof dish with a little butter.: Greasing creates a thin, glossy film that helps juices caramelize against the dish walls, producing sticky, flavorful edges. When the butter melts you may smell it taking on a light toasted note, which deepens during baking. If you skimp on greasing, the fruit can stick and the edges will not caramelize properly. Use just enough butter to coat the base and sides so the fruit can slide slightly as it bubbles.
Roughly chop approximately 2-3 cups of feijoa flesh and pop it in the bottom of the greased oven proof dish.: As you chop, the feijoa will release a lively perfume that hints at its tart sweetness. Spread the flesh evenly in the dish so the filling cooks uniformly and forms a consistent jammy layer. A frequent misstep is overcrowding the dish, which prevents even heat circulation and can leave parts undercooked. Aim for an even layer rather than piling the fruit high.
Add vanilla and honey to the fruit and mix through.: Mixing incorporates the vanilla essence and honey so their flavors distribute evenly, and you may notice the mixture gleaming slightly as the honey coats the pieces. This step helps the fruit develop an even sweetness and supports caramelization. Stir gently to avoid smashing the fruit into a puree; overmixing will remove the pleasant texture contrast between bits of fruit and softer areas.
In a food processor place the oats, almonds, flour, brown sugar and butter, blitz until you have a nice crumbly topping.: The sound of the processor will change from coarse chopping to a whispering blend as the butter combines with the dry ingredients, and you should see a mixture of coarse crumbs and small clusters that will crisp beautifully. This texture is critical, because it yields both crisp shards and tender pockets. Avoid overprocessing into a paste, which makes the topping dense rather than flaky. Pulse in short bursts and check frequently to reach that ideal crumb.
Top the fruit with the crumble topping, bake for approximately 20 mins until the feijoa crumble is golden and crunchy.: As it bakes you'll smell the almonds toasting and the butter caramelizing, and you should see the topping turn an even golden brown with bubbling fruit juices at the edges. The contrast between the bubbling filling and the crunchy top is your cue that it's done. If the top browns too quickly before the fruit is bubbling, lower the rack or tent loosely with foil to prevent burning while the center finishes cooking.
Serve with a little vanilla ice cream, cream, yoghurt or custard.: The final texture juxtaposition of warm, slightly tart fruit with creamy, cold accompaniment is incredibly satisfying, and the melting dollop will mingle with the juices to create silky spoonfuls. Taste and decide if a touch more honey is needed, but be mindful that accompaniments add sweetness. A common pitfall is serving it too hot, which can make the topping lose its crispness quickly; let it rest for a few minutes so the filling sets slightly before plating.
