Which is, naturally, the lemon curd. I snapped a few pictures to illustrate the process, so here they are:
1) Assemble your ingredients. You need 4 egg yolks, 2 tsp lemon zest, 4 tbsp butter, 3 fl. oz. freshly squeezed lemon juice, and (not pictured) 3/4 c sugar and a pinch of salt.
2) Beat the egg yolks and sugar together. Add all the other ingredients EXCEPT for the lemon zest; mix, and put on the stove on low heat. Stir constantly.
3) Have the lemon zest waiting in a bowl. Have a strainer waiting so that when the mixture has thickened, you can strain it directly into the bowl.
4) Once the mixture has cooled off a bit (give it a stir every once in a while), pour into pre-baked tart shell and bake at 300 for 7 minutes (it will still be jiggly-wiggly).
5) Here's what mine looks like! Yummo! I could eat lemon curd straight out of the bowl - yes, all of it - so I had better get going on the blueberry topping before it all disappears!