To begin, preheat your oven to 400 degrees and bring a pot of water to a boil. Trim the brussels sprouts and half them, then add them to the boiling water and blanch the vegetables for 2-3 minutes or until the sprouts are bright green. Strain the sprouts.
Using a paring knife, hollow out the inside of the brussels sprouts cut side, setting the inside leaves aside. Once all the middles are carved out, chop the reserved inside leaves.
In a skillet heat extra-virgin olive oil on medium-high heat and add the chopped leaves and two chopped cloves garlic. Saute 3 minutes then remove from heat. Stir in the ricotta, panko bread crumbs, parmesan cheese, rosemary, and sage. Season with kosher salt and black pepper.
Scoop the filling into the brussels sprouts using a small spoon and place on a greased baking sheet. Place in the preheated oven and bake until sprouts are crispy and the filling is warm; about 20 minutes. Remove from oven and serve.