Creamy Lemon Crumble Bars

make the creamy lemon filling (you can do this a day in advance)

1. Put the lemon juice, egg and yolks, sugar, and salt in a 2-3 quart heavy bottomed saucepan. Whisk to combine.
2. Add the butter and begin heating on medium to medium high, whisking almost constantly.
3. As the butter melts, switch to a silicone spoonula and continue stirring, scraping the sides and bottom of the pan as the mixture begins to thicken. When it comes to a gentle bubble, stir for a few seconds more, then remove from the heat.
4. Push the curd through a strainer, pressing down with the back of your silicone spoonula to get as much through as possible. You'll just be left with a few small lumps of cooked egg. Chill until cold.
5. Once the curd is cold whisk in the heavy cream.

for the crust and crumble

1. Preheat the oven to 350F. Line a 9x9 inch square baking pan with parchment paper with long ends so you can lift it out for neater slicing. Note: this step is completely optional: you can serve the lemon bars right from the pan if you prefer.
2. Cream the soft butter and sugar until light and fluffy, about 3-4 minutes, scraping down the sides of the bowl as necessary. Beat in the vanilla paste and salt. Note: it's important that your butter be at room temperature. I like to leave it out overnight when I know I'll be baking.
3. With the mixer on low, slowly add the flour and mix just until there is no dry flour left. Don't over mix.
4. Take 2/3 of the dough and pat it into the bottom of your tart pan. I like to scatter the dough in crumbles across the bottom, and then start to pat it down. It helps to flour your fingers, or use the bottom of a metal measuring cup to tamp it down. Take the time to get the dough evenly distributed. Note: you're not looking to go up the sides of the pan with the dough, just to make an even flat layer.
5. For the crumble topping ~ mix the remaining dough with the rolled oats, breaking it apart with your fingers to make coarse crumbles.
6. Spread a layer of creamy lemon filling over the top of the bottom crust. You'll use about a cup. (Note: you will have a little extra creamy lemon curd leftover to use on toast or scones.)
7. Top evenly with the crumbled dough. It's fine if some of the lemon shows through.
8. Bake in the preheated oven for about 40 minutes, or until the top is just starting to turn pale golden.
9. Let the pan cool on a rack. If you've used parchment paper, let the pan cool for about 20 minutes, then you can gently lift the bars out of the pan for slicing.
10. Serve warm or at room temperature. The bars will keep on the counter for 2-3 days, and can be frozen for longer storage.