Preheat the oven to 175 degrees Celsius / 350 degrees Fahrenheit (top and bottom heat).
First, we'll make the crumb topping. Place all the ingredients in a bowl and rub them together with your fingers until the mixture is crumbly. If needed, add one or two tablespoons of cold water to help the mixture come together more easily. Then, place the mixture in the refrigerator.
For the cake, place the butter and sugar in the bowl of a stand mixer. Beat for about five minutes, until the mixture is light and fluffy.
Next, add the eggs one at a time. Then, add the flour, baking powder, full-fat yogurt, lemon zest, and a generous pinch of salt.
Pour the batter into a greased sheet pan.
Using a spoon, dot the lemon curd over the cake. Swirl it through with a skewer to distribute the lemon curd throughout the cake.
Sprinkle the crumbs over the cake.
Bake for 45–60 minutes or until done. Insert a skewer into the center. If it comes out clean, the cake is done.
Optional: Dust the cake with powdered sugar for decoration after baking. Enjoy!