Preheat your oven to 350°F (175°C) and prepare your muffin tin by greasing or lining with parchment.

Cream together the softened unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes.

Gradually add the all-purpose flour (or chosen gluten-free alternative) and salt, mixing until crumbly.

Press the crust mixture evenly into each muffin tin cup, ensuring it's well-packed.

In a saucepan, combine chopped rhubarb, a bit of sugar, and lemon juice over medium heat. Cook for 5-7 minutes until soft and syrupy.

Whisk egg whites until frothy, then gently fold in sweetened shredded coconut, vanilla extract, and a pinch of salt.

Spoon the warm rhubarb filling over each crust, then add dollops of coconut mixture on top.

Bake for 20-25 minutes until tops are golden brown and crisp.

Remove from oven and allow to cool in the tin for 15-20 minutes before serving.