Rhubarb Berry Curd Macarons

From 6 Bittersweets Guest Post
Filling adapted from Lara Ferroni
Makes about 25 to 35 macarons

XIAOLU'S NOTES: Please do not try to convert this recipe to volume measurements if you don't have a scale (I use and love this one). This recipe is very sensitive and will not work if the measurements are not exact. Please also note that every oven is different and you'll figure out what works best for yours over time (see this post for great information on ovens and macarons). Since mine has major hot spots, I bake on 2 stacked pans for insulation. If you're uncertain of your ability to pipe uniformly-sized macarons, like me, simply trace 1 1/4-inch circles on your parchment paper, flip the paper over, and pipe on the other side, using the outlines as your guide OR print (choose "fit to page") and slide this template under your parchment as a guide but don't forget to remove before baking! See my first macaron post for helpful videos of the whole macaron-making process!

120 g almonds [not roasted or salted]
150 g powdered sugar
5 to 8 g freeze-dried strawberries (optional)
1/4 tsp salt
35 g granulated sugar
2 g egg white powder [optional, to stabilize batter in humid weather]
95 to 100 g egg whites [about 3 large egg whites]
1/8 tsp cream of tartar or 1/4 tsp lemon juice [optional, to stabilize meringue]
Red or pink powder or gel food coloring (optional)
1 to 1 1/2 cups Rhubarb Berry Curd [Recipe below]

Microwave fresh egg whites 10 to 15 seconds in the microwave on medium heat.

Combine the almonds, powdered sugar, freeze-dried strawberries, and salt in a food processor, and pulse on and off until the nuts are finely ground (about 1 to 2 minutes). Sift the powder to remove any large chunks that remain. Put those chunks back into the food processor and pulse again for another 30 to 60 seconds. Sift again. You will probably have some slightly chunkier almond bits. Hopefully they're no more than a tablespoon or so, in which case you can throw them out.

Weigh out and mix your granulated sugar and egg white powder in a small bowl until uniform; set aside. Using a handheld or stand mixer, whip the egg whites on medium-low speed with cream of tartar until foamy, then turn the speed up to medium to medium-high and gradually add the sugar mixture. Add a small amount of food coloring and continue whipping until you obtain a glossy meringue (it'll look like shaving cream, hold stiff peaks, and stay in place if you turn the bowl upside-down; but don't overbeat your meringue or it will be too dry).

Add all of the nut mixture to the meringue and fold together. Use both a folding motion that scrapes the bottom of the bowl (to incorporate the dry ingredients) and a gentle pressing motion, to deflate the meringue against the side of the bowl. Slow down after all the dry ingredients have been incorporated, and continue folding the mass carefully until you obtain a batter that looks somewhat glossy and flows from the spatula in a thick ribbon.Test the batter by spooning a small amount of the batter up, then dropping it back down on itself. It shouldn’t disappear immediately, but if it melts back into the rest of the batter within 20 seconds, it's ready for piping (this page has a nice photo of this test). If not, fold 2 more strokes and test again.

Fill a pastry bag fitted with a 1/3 to 1/2-inch wide plain tip (I like Ateco #804 or 806) with half of the batter. (When your bag is too full, the pressure causes the batter to rush out in a way that’s difficult to control, making for sloppy macarons.) Pipe tiny blobs of batter onto the 4 corners and center of 2 baking sheets, then line baking sheets with parchment paper OR line with silicone mats. Pipe small rounds (slightly larger than 1 inch wide) straight down and about 1 inch apart onto the baking sheets. Pick up each sheet with both hands and slam it firmly straight downward on the counter 2 to 3 times. This will to force out any large air bubbles. Immediately pop any bubbles that rise up but don't break with a toothpick. Do NOT do this once a few minutes have passed because you'll mess up the shell that's forming.

Preheat the oven to 285 to 300 degrees F. Let the macarons sit out for 25 to 90 minutes to harden their shells a bit (to prevent tops from cracking during baking). Test if they're ready by touching the top and side of one shell lightly. It should feel dry and not stick to your finger at all. Bake one pan at a time for 15 to 25 minutes, depending on the size of the macarons. After the first 10 minutes of baking, rotate the pan and place a large piece of foil loosely over the macarons to prevent browning (do NOT press foil down). Let cool completely before trying to move the shells.

Once cool, flip the shells over. If you have trouble removing them from parchment paper, pour a couple of drops of water under the paper while the sheet is still a bit warm, and the macarons will lift up more easily due to the moisture. Don't let them sit there in it too long or they will become soggy.

Fill the shells (spooning or piping) with 1 1/2 to 2 teaspoons curd and top with a similarly-sized top shell. For the best flavor and texture, store in the refrigerator for at least 6 hours before eating (shorter time since this filling is so moist) but these are best if eaten within 3 days. Bring to room temperature before eating.

Rhubarb Berry Curd
Makes about 12 oz.

10 oz. rhubarb, chopped
4 oz. raspberries OR chopped strawberries, fresh or frozen
9 Tbsp sugar
6 large egg yolks
1 Tbsp cornstarch
Pinch of salt
1 tsp lemon zest
3 1/2 Tbsp butter, cut into pieces

Stir the rhubarb, berries, and 1/4 cup of sugar together in a medium sized pot. (Since I was using frozen raspberries I didn't add any water, but if you are using fresh, you can use about 1/4 cup of water.) Cook over low heat until you can no longer see whole pieces, and it looks like a largely uniform sauce. Let cool and puree the sauce in a traditional or stick immersion blender. Then strain puree to remove the berry seeds.

In a double boiler (or a bowl over simmering water), whisk the egg yolks, cornstarch, remaining sugar, and salt. Whisk until well combined and warm. Add about 1 cup of the rhubarb sauce and the lemon zest and stir until well combined. Check for taste and add more of the pureed rhubarb until you get the desired flavor and color. Contiue cooking and stirring until thickened. Remove from heat and stir in the butter a piece at a time until is melts and disappears into the curd. Let cool to room temperature, then store in the refrigerator until ready to use.