Slice off the stem and green leaves from the Leek (2), and quarter them vertically.
Place the leek into a large bowl of cold water. Agitate the pieces to make sure any dirt falls to the bottom of the bowl. Let sit for 5 minutes.
Clean the Shiitake Mushroom (0.5 pound) and Cremini Mushroom (1/2). Remove the stems.
Thinly slice the mushrooms and set aside.
Drain and rinse the leek, and thinly slice. Set aside.
Drain the Jarred Roasted Red Peppers (2) before chopping. Set aside.
Finely chop the Garlic (3 clove). Set aside.
Pick off 5 to 6 leaves from the Fresh Sage (1 bunch) and finely chop. Set aside.
Heat a large pan over medium-high heat. When hot, add Olive Oil (1 tablespoon) and the leeks. sauté for 3 to 4 minutes until they have a little color and begin to soften.
Add mushrooms and peppers and sauté for 5 minutes.
Add the garlic and sauté until fragrant.
Add in the Heavy Cream (2 tablespoon) and Sherry Vinegar (2 tablespoon). Bring to a boil and simmer until all the liquid has evaporated, about 10 minutes. Halfway through add in the chopped sage. Remove the pan from the heat.
Preheat your oven to 350 degrees F (180 degrees C).
Prepare the Parmesan Cheese (1/2 cup) using a microplane, and use a box grater for the Gruyère Cheese (1/2 cup).
Add the mushroom mixture to a mixing bowl, and fold in the both cheeses.
Using pieces of the Crescent Roll Dough (2 sheet), add about a tablespoon of the mixture. Begin by folding one side over the other.
Fold the dough around the other sides to make sure the filling is completely covered.
Pinch the dough together at the base. If there’s excess dough, trim it off. The trimmed off dough can be used to make another wrapper. Each can of crescent dough should make 8 to 10 depending on how much filling you are putting in.
Take a few sprigs of sage and lightly hit them with the back of your knife. In a microwave safe bowl, add in the sage and Unsalted Butter (2 tablespoon). Microwave for 30 to 45 seconds until melted.
Place the buns on a parchment lined sheet pan with 2-inches between them. With a knife, lightly make an "x" on the top of the bun. Brush them with the sage butter, and place them in the oven for 15 minutes, or until golden. Rotate pan(s) halfway through.
As the buns bake, make the sauce. Peel and grate the horseradish (1 inch).
To a bowl, add the Sour Cream (1 cup), Horseradish (1 inch), half the Lemon (1) zest, Freshly Ground Black Pepper (to taste) and a teaspoon of lemon juice and mix together. Taste to see if it needs Kosher Salt (to taste), Freshly Cracked Pepper ( to taste) and Lemon (1 N/A) juice.
Once the buns are finished cooking, place them on a rack to cool for a few minutes before serving. Serve with horseradish crema and enjoy!