Preheat the oven to 325 degrees. Spray a mini muffin tin with vegetable spray and set aside.
In a small bowl, mix together the flour and salt. (if you have vanilla powder, mix it into the dry ingredients. If you're using vanilla extract, add it with the sugar and butter mixture) Set aside.
Add the butter to a large mixing bowl and beat on medium speed with electric mixer to a creamy consistency. Add the powdered sugar and beat for 1-2 minutes until pale yellow and fluffy. (If using vanilla extract, add it here.)
Add the flour to the butter mixture and beat on low speed until incorporated, scraping down sides of bowl as necessary.
Scoop 1 level tablespoon of dough into each muffin tin. Use floured dough tamper, to tamp the dough into the muffin tin to form little shells. Refrigerate for 10-15 minutes until chilled.
Bake for 10 minutes remove from oven and use your dough tamper again, to press the puffed dough down into the shell. Bake another 5-8 minutes until golden brown. Allow the shortbread shells to cool in the pan. Carefully slide a very thin knife between the tart and the pan and remove the shortbread crusts. (Shortbread is naturally crumbly, so don't worry if a little cookie falls away (I call these chef's tastes). Cool to room temperature on a wire rack.
When shells are at room temperature, pipe or spoon curd into the shortbread shells. Top with a piece of kiwi, or other fruit and mint leaves for garnish. Cover loosely with plastic wrap until ready to serve. Best if served the same day.