Preheat the oven to 350℉/180℃
Simmer the raspberries and sugar together in a small pan until the raspberries are soft enough to mash.
Create a slurry with the cornstarch and water, and add this to the raspberry/sugar mixture. Simmer for a few minutes until thickened, then let cool. (You can strain if you prefer no seeds).
Cream the butter, lemon zest, and caster sugar together until light and fluffy.
Beat in the eggs one at a time, then gently fold in the flour and lemon juice until well combined.
Fill 24 cupcake liners halfway, then add ½ teaspoon of the raspberry sauce to each and swirl with a toothpick.
Bake for 15-18 minutes. You can check whether they are done by testing whether a toothpick comes out clean (I recommend testing the largest one if unequal).
While the cupcakes are baking, mix together the sugar and lemon juice to create the lemon drizzle.
Let the cupcakes cool for at least 10 minutes if you prefer a slight crunch. Otherwise, you can immediately prick the cupcakes with a toothpick and drizzle the lemon/sugar mixture over the top of each cupcake with a spoon.
Enjoy! (This is a very important step, be sure not to skip it).