Preheat oven to 400°F / 200° C / Gas mark 6. Place four 16 ounce baking dishes (or one 8x8 baking dish) on a baking sheet and set aside.
In a medium bowl, combine seeded loquats with lemon juice and toss to combine. (Or, add lemon juice to bowl and drop seeded loquats into it as you're working to keep them from turning brown)
Add sugar, cornstarch, vanilla and nutmeg to the loquats. Toss well to combine and divide evenly between baking dishes (or pour into one baking dish).
Make biscuit topping in a separate medium bowl - toss together flour, sugar, baking powder and salt.
Using a pastry blender, cut butter into the flour mixture until it resembles coarse crumbs. Pour in whole milk and stir with a fork until it comes together.
Drop spoonfuls of biscuit topping over prepared loquat filling, covering most of the fruit.
Sprinkle with sanding sugar, if desired.
Make for 30 - 35 minutes, until golden brown and bubbling. Cool slightly before serving.