For the strawberry jam filling: place the frozen berries (12 ounces/340g) in a saucepan and warm over low heat until softened, about 5 minutes. Add the granulated sugar (¼ cup/50g) and mix until combined. Use a fork to crush the strawberries. {Be sure to smash them so they won’t be in large pieces in the strawberry rolls).
Dissolve the cornstarch (2 tablespoons/16g) in the water (2 tablespoons/30mL), then add it and the vanilla (1 tablespoons) to the crushed strawberries. Bring to a low boil and cook for 5-6 minutes until the mixture has thickened. Remove from the heat and allow to cool while you prepare the cinnamon roll dough {can be prepared up to one day ahead, store covered in the refrigerator}
Remove 2 tablespoons of the strawberry filling and set it aside for the strawberry cream cheese icing.
For the cinnamon roll dough: (I like to turn on my Breville toaster oven to 120°F while I am mixing and kneading the dough. Turn it off when it reaches temperature and keep the door closed. This creates a warm environment for letting the dough rise)
In the bowl of a stand mixer add the warm kefir (¾ cup/180mL), sugar (¼ cup/50g), yeast (1 tablespoon/10g) and melted and slightly cooled unsalted butter (¼ cup/56g) and give it a little stir. Let the mixture sit for 10 minutes.
Add the eggs (2 large), bread flour (3 cups/390g) and kosher salt (1 teaspoon), and beat at medium speed (4 on KitchenAid mixer) with the dough hook until a soft dough forms, about 8 minutes. If the dough is sticking to the sides of the bowl after 4-5 minutes, add up to 3 tablespoons of additional flour. *If you do not have a stand-mixer with a hook attachment, knead the dough by hand in this step. You can see this post for the how to. When kneading by hand, add flour as necessary, but try to add as little as possible. (I typically use less than 3 tablespoons flour for kneading)
Grease the bowl you mixed the dough in (no need to wash it) and place the dough in the bowl, cover and let rise about 1 hour, or until double in size. (I place it in the slightly warm toaster oven)
While the dough is rising, prepare the baking pan. Grease a 9×13 baking pan with butter or cooking spray and set aside or line the pan with parchment paper.
Remove the dough from the bowl and roll it into a rectangle on a lightly floured surface. I like the narrow side to be about 12 inches and the long side about 16-18 inches.
Spread the strawberry jam filling over the dough, covering almost to the very edge {use about ¾ cup of jam, you will have some leftover}. Then sprinkle the cinnamon (2 teaspoons) over the strawberry jam. Tightly roll the dough starting from a long side until you create a log. Using dental floss***(or clean thread), cut the log into 12 equal pieces and place them in the prepared pan. Alternately, you can cut 12 long strips of dough and roll each length of dough individually or cut them traditionally and place them in a buttered muffin pan (they will bake faster in a muffin pan; check them at 12 minutes).
Place the dough back in your warm spot and allow it to rise a second time, about 30 to 45 minutes until the rolls have doubled in size (if your kitchen is warm, it may not take this much time). When the strawberry cinnamon rolls are close to the end of the second rise, preheat the oven to 350°F.
Bake for about 18-25 minutes, until the edges are lightly brown. If you want to check by temperature, the sweet rolls internal temperature should be 190°F.
When the rolls are done, remove the pan from the oven and place the pan on a wire cooling rack. Allow to cool for a couple minutes while you prepare the glaze.
Using a hand mixer or stand mixer, beat the butter (2 tablespoons/28g) and cream cheese (¼ cup/2 ounces/ 56g) until combined, about 1 minute. Add the confectioners’ sugar (1 ½ cups/180g) and mix on low until combined, then increase the speed until a thick frosting forms, about 2-3 minutes. Then add 2 tablespoons of the reserved strawberry filling and beat on medium until fully mixed in.
Spread the strawberry cream cheese frosting over the warm rolls. Top with fresh or freeze dried strawberries (if desired) and enjoy!
