Add yeast to warmed milk in liquid measuring cup and whisk to dissolve. Let rest 5 - 10 minutes.
Meanwhile, add sour cream, granulated sugar, salt, egg, vanilla extract, vegetable oil and melted butter to bowl of electric stand mixer.
Add milk mixture. Set stand mixer with whisk attachment and blend mixture to combine.
Add in 1 1/2 cups flour and blend until combined, then switch to hook attachment and slowly add in remaining 1 1/2 cups flour.
Knead mixture until smooth an elastic, about 5 minutes, adding in additional flour as needed to create a soft dough (it should pull away from sides of the bowl and may slightly stick to the bottom).
Transfer to a lightly oiled bowl, cover with plastic wrap and allow to rise in a warm place until double in size (I like to place it in the oven with the light on), about 1 1/2 - 2 hours.
During the last few minutes of rising, grate apple and place in a bowl then toss with lemon juice and set aside.
In a separate small mixing bowl, whisk together brown sugar, cinnamon and nutmeg, set aside. Punch dough down. Roll out onto a clean, lightly floured work surface to about an 19 x 13 inch rectangle.
Brush top evenly with 1/4 cup butter and sprinkle with cinnamon sugar mixture and spread into an even layer.
Squeeze 6 Tbsp of the excess liquid from apples into mixing bowl by lifting and pressing grated apples against sides of bowl (or just squeeze in your hands) and reserve juice (you'll be using most of it for the glaze). Sprinkle strained apples evenly over cinnamon sugar layer.
Beginning on the long side (the 19-inch side) snuggly roll up to the other end (to the other 19-inch side, this may seem like the wrong side to be rolling, I usually begin with the shorter side, but it works best this way as you want taller not wider rolls for the muffin tins).
Cut into 12 - 13 rolls and transfer each rolls to paper lined muffin cups that have been sprayed with non-stick spray (preferably use 2 - 12 hole muffin tins to allow muffin tops room to expand outward).
Cover loosely with plastic wrap and allow to rest in a warm place 40 minutes, preheating oven to 375 during last 10 minutes of rising.
Brush tops of rolls lightly with butter, then bake in preheated oven 14 - 17 minutes until lightly golden and centers are no longer doughy.
Allow to cool slightly then drizzle with glaze and enjoy warm. Store in an airtight container (preferably rewarm in microwave 10 - 20 seconds before enjoying).
For the glaze: In a mixing bowl whisk together 3 tbsp reserved apple juice, powdered sugar and 1/2 tsp vanilla extract. Add in more apple juice as needed 1 tsp at a time until desired consistency is reached.