• If using fresh rhubarb, dice 4-6 rhubarb stalks into small slices (just as you would if dicing celery) (yields 2 cups diced rhubarb).

  If using frozen rhubarb, pour 2 cups of rhubarb into a strainer and place the strainer in the sink. Allow the frozen rhubarb to thaw and drain (takes 1-2 hours). Place the drained rhubarb onto a paper towel and pat dry.
• Place the sour cream and eggs on the counter and allow to come to room temperature (takes 1-2 hours).
• Heat the oven to 350 degrees Fahrenheit.
• Generously grease a 9x5 inch loaf pan with butter before adding the batter to prevent it from sticking.
• In a large mixing bowl combine ½ cup (1 stick) of softened (but not melted) unsalted butter and 1 cup of sugar. Cream the butter and sugar together for a minute using a hand mixer or the paddle attachment of a stand mixer on medium speed until light and creamy.
• Add the 2 large eggs and ½ cup of full fat sour cream OR plain Greek yogurt to the bowl. Mix together for another 30 seconds on medium speed.
• In a second mixing bowl combine 2 cups of a gluten free flour blend, 1 tsp. baking powder, 1 tsp. baking soda, and ¼ tsp. of kosher salt. Mix together with a fork until combined.
• Add the dry ingredients to the wet a bit at a time, stirring each time with a spatula. Continue until all of the dry ingredients are added and stir until completely combined.

  The batter will be thick and dense.
• Add the diced rhubarb to the batter and fold it in until combined.

For The Streusel:

• Cut 2 Tbsp. of cold, unsalted butter into cubes and place in a bowl. Add 4 Tbsp. of light brown sugar, 3 Tbsp. of gluten free flour blend, 1 tsp. cinnamon, and ¼ tsp. of kosher salt.
• Using a pastry cutter, combine all of these ingredients until the mixture resembles coarse crumbs (this may take a few minutes).
• Zest 1 lemon using a Microplane or small zester and add the zest to the bowl. Stir until combined using a fork.
• Pour half of the batter into the pan and smooth it down with a spatula.

  Pour the streusel evenly over the batter.

  Pour the remainder of the batter on top of the streusel and smooth it with a spatula. The batter is very dense and it may take a little effort to even it out.
• Place the bread pan into the oven. Bake for 60-65 minutes.

  The bread is done when a toothpick inserted into the center comes out clean.
• Remove the pan from the oven and allow the bread to cool completely.
• To Serve: Cut the cooled bread into slices and serve with butter or toppings of choice (optional).