1 cup butter, room temperature
¾ cup sugar
1 pound rhubarb stalks, trimmed
1¼ cups all-purpose flour
¾ cup blanched almonds
1 teaspoon baking powder
½ teaspoon kosher salt
½ tablespoon vanilla paste or vanilla extract
2 large eggs
¼ cup plain Greek yogurt or sour cream
extra butter and sugar for greasing the pan and sprinkling on the surface
You’ll need an 11 x 8” rectangular tart pan or 10” round tart pan with a removable bottom. I used a 9″ round pan and it overflowed the edges a bit as it baked, which just needs to be trimmed off before you try and remove it from the pan. You can substitute a springform pan but you lose the pretty fluted edges that the tart pan gives you. Or, if all else fails, line an equal-sized pan with parchment paper, leaving enough of an edge to hold on to later, and once the cake has cooled, lift it out very carefully using the edges of the parchment.
Preheat oven to 350°. Butter the tart pan, making sure to get into all the little creases, and sprinkle generously with sugar, tapping out excess. Or if you’re using a regular pan, line it with parchment paper first and then butter and sugar the inside of the paper as this gives the cake a nice crunch on the outside! Slice the rhubarb in half lengthwise (quarter if very large). Measure 6-8 of the prettiest pieces to make sure you have enough for the top of the cake and set aside; chop remaining rhubarb into ½” pieces. It’s OK to piece the strips together if they’re not long enough.
Pulse flour, almonds, baking powder, and salt in a food processor until almonds are finely ground (texture should be sandy). Check the texture before you continue, and if the almonds are still chunky, give it one more minute in the food processor.
Place butter and sugar in a large bowl. Add vanilla paste or extract, mix until blended. Using an electric mixer on high speed, beat until light and fluffy, about 2-3 minutes. Add eggs, one at a time, beating to blend first egg before adding the second. Beat until mixture is pale and fluffy, another 2 minutes. Reduce speed to low and gradually add dry ingredients, followed by yogurt. Mix, scraping down the sides of the bowl as needed, just to combine (batter will be thick). Fold in chopped rhubarb and scrape batter into prepared pan. Smooth batter and arrange reserved rhubarb over top; sprinkle top evenly with another 3 tablespoons of granulated sugar.
Place tart pan on a large rimmed baking sheet (to catch any rogue juices) and bake, rotating once, until cake is golden brown and rhubarb on top is soft and beginning to brown, about 60 minutes. Transfer to a wire rack and let the cake cool before removing from pan.
Do Ahead: Cake can be baked 3 days ahead. Keep tightly wrapped at room temperature.