Preheat your oven to 350 degrees. Grease and line the base and sides of a 6" spring-form tin with parchment paper.
Using a food processor, add the flour, baking powder, and sugar, and cold butter (cut into small chunks), and pulse until fine crumbs. Add the lightly beaten egg and continue to pulse until it just comes together. You do not want it to be a ball, but still a crumb-like mixture.
Remove the mixture using a spatula, turning it out onto a piece of plastic wrap. Gently form it together, then using a knife, divide the mixture into thirds. Set aside ⅓ of the mixture for the topping. Press the remaining ⅔ of the mixture into the bottom of the prepared springform pan.
Heat up the lemon curd on the stovetop or in the microwave so it is warm, and spread it over the cake mixture.
With the remaining dough, crumble it with your fingers over the lemon curd.
Bake for 30 minutes until golden brown.
Remove the pan from the oven and cool completely. Take a knife and scrape it around the outside of the cake, the inner part of the springform pan, to loosen the cake. Remove the tin.
Pull away the parchment paper, and place the cake on a serving platter. Dust with powdered sugar and serve. Optional to serve with fresh whipped cream or vanilla ice cream and a tiny mint sprig.