Place a small braiser or medium dutch oven over medium heat. Add the butter and olive oil to the hot pan and melt. Add the shallot, fennel, beet and 1/2 teaspoon salt and cook, stirring often, until fragrant and the vegetables are beginning to soften, about 3 minutes. Add the rice and stir to coat the in butter and oil mixture and toast slightly, about 3 more minutes. Deglaze with the sherry vinegar and season with the remaining salt. Begin adding the broth, 1 cup at a time, stirring often. Cook, stirring, after each addition until the broth is almost completely absorbed, continuing with the remaining broth until the risotto is creamy, cooked through and still moves slightly when spooned onto a plate. This will take about 20 minutes. Stir in the Parmesan until melted. Serve with crumbled gorgonzola on top.