This rhubarb coffee cake, with a sweet and crunchy streusel topping, comes together easily in mere minutes, and is great to have around for snacking, breakfast, or a little sweet bite at the end of a meal.
Preheat the oven to 350 degrees F. Grease and flour an 8 x 8 inch square baking pan
In a food processor (or using a bowl and fork), pulse 1/2 cup flour, 2/3 cup brown sugar, 1/4 cup butter, and salt, until crumbly (30 seconds or so).
In a medium mixing bowl, whisk together the flour, baking powder and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar on medium speed (about 3 minutes).
Add the eggs, sour cream and vanilla, and beat to combine, scraping down the bowl as needed (about 2-3 minutes).
Add the flour mixture and mix on low speed until just combined. The batter will be thick.
Remove the bowl from the mixer and fold in the rhubarb until evenly distributed.
Spread the batter evenly into the prepared baking pan and bake in the preheated oven for 45-60 minutes, until a toothpick inserted in the center comes out clean. Serve at room temperature, or slightly warm.