In a heat-proof measuring cup, whisk together the milk, yogurt and sugar, microwave about 30 seconds, or until it reaches 110℉. If it becomes too hot, cool to 110℉. Add yeast and stir, let sit 10 minutes.
In the bowl of a stand mixer fitted with the paddle attachment, add the flour, salt and protein powder. Mix briefly.
Add in the milk mixture, egg, and melted butter. Mix on medium speed until a soft dough forms. Switch to the hook attachment and beat on medium speed, about 5 minutes, until dough becomes completely smooth and elastic. It’s ok if it’s a little tacky, but we don’t want a dry dough, or one that’s overly sticky. If you don’t have a stand mixer, use a wooden spoon and bring dough together in a large glass mixing bowl, turn out onto a floured work surface and knead by hand vigorously for about 5 minutes until dough becomes smooth and elastic. Cover and let the dough rise in a warm place in your kitchen until dough is puffy and almost doubled in size, about 40-60 minutes.
Make the frosting: In a medium bowl, beat the neufchatel cheese with an electric hand mixer until smooth. Add remaining ingredients and beat until combined. Taste and adjust sweetness level if desired.
Mix the brown sugar and cinnamon for the filling together in a small bowl.
Lightly grease a 13”x9” baking dish. Once dough has risen, punch down and place on a floured work surface. Roll out into a rectangle approximately 16”x10”. Spread the butter over the dough, followed by the brown sugar and cinnamon, leaving a ½” bare edge on one long side. Roll tightly toward the bare edge side to form a log, seal by pinching the seam,
Cut into 12 uniform slices using dental floss or a serrated knife. Place rolls into prepared baking dish. Cover with plastic wrap and let them rise until puffy, about 30-45 minutes.
Preheat oven to 350℉. Once preheat, place rolls in oven and bake 20-25 minutes, or until golden brown and cooked through. Do not overcook. Cool 15 minutes, frost, and serve.