Cold Buttermillk Soup with Cardamom Rusks and Rhubarb Compote

Directions

1. Preheat the oven to 350. Line two baking sheets with parchment paper.
2. The first step is making the kammerjunker and this should ideally not be done on a hot day! In a stand mixer or with a sturdy spoon, beat the butter and sugar together until light and fluffy. Add the egg and mix until incorporated and then add the milk and mix well. In a separate bowl, whisk together the flours, cardamom, salt, and baking powder. Next, add the oats and lemon zest to the flour mixture and stir together. Dump the dry mixture into the wet mixture and mix until combined. If your dough is really soft and sticky and you've got time to spare or something you need to do, you can chill it in the fridge for 20 minutes. Otherwise, proceed!
3. Dump your dough onto a lightly floured countertop and roll into a log with about a 1" diameter. Cut the log into even-size pieces and roll into balls. You can also skip the log rolling and just grab pieces of dough and roll them into balls. Either way, the goal is to have balls the approximate size of walnuts. Place the balls, evenly spaced on your prepared cookie sheets and bake for 10 minutes
4. After 10 minutes, check your rusks. If they are really soft and doughy still, you can bake them for another 2 minutes. Otherwise, take them out and turn the oven down to 275. Immediately cut the rusks in half with a small serrated knife. Place the halves cut side up on your baking trays and return the trays to the oven. Bake for 30 more minutes or until golden brown. Place the rusks on a rack to cool and then put them in an airtight storage container. In theory they will keep for weeks but in my house we devour them too quickly!
5. To make the cold soup, scrape the seeds of the vanilla bean into a bowl and add the sugar. Mix well then add the egg yolks and beat until pale and fluffy. If you are concerned about consuming raw egg you can use pasteurized egg yolks here or pasteurize the yolks yourself using your microwave (I've seen instructions for this online). Add the lemon juice and zest and mix well. Add the buttermilk and milk, stir until well blended. Transfer to a storage container (I like a pitcher or a Weck juice jar), and chill for at least 2 hours.
6. Place the sliced rhubarb into a small saucepan with the sugar and turn the heat to medium. Cook stirring regularly until the rhubarb releases water and starts to break down. At this point, you can turn the mixture down to a simmer and leave it partially uncovered to cook down. Stir occasionally to keep the bottom from sticking. It's ready when then mixture is thick like applesauce. Let cool to room temperature, then cover and refrigerate until you are ready to eat it.
7. When you are ready for breakfast, pour yourself a bowl of buttermilk soup, put a dollop of rhubarb in the middle, and crumble a few rusks on top. Stir together and eat immediately.