How to Make It
Wrap cheese rinds together in cheesecloth; tie securely using kitchen twine. Place wrapped rinds and 6 cups water in a large saucepan; bring to a boil over medium-high. Reduce heat to medium-low; simmer, uncovered, until reduced to about 4 cups, about 30 minutes. Remove wrapped rinds; discard.
While cheese mixture simmers, heat polenta in a large skillet over medium-high. Cook, stirring often, until polenta is lightly toasted and smells nutty, 5 to 6 minutes. Transfer polenta to a medium bowl; reserve 1 teaspoon polenta for garnish. Set aside.
Return cheese-infused water to a boil over medium-high. Slowly add toasted polenta, whisking constantly to prevent clumping. Cook, whisking constantly, until polenta starts to thicken and bubble, 3 to 4 minutes. Reduce heat to low, cover, and cook, whisking vigorously and scraping bottom of pan every 5 to 10 minutes, until polenta is thickened and tender, 50 minutes to 1 hour, whisking in up to 1/2 cup remaining water as needed to loosen. Whisk in salt.
During final 10 minutes of polenta cook time, fill a small saucepan with water to a depth of 1 inch; bring to a simmer over medium. Stir together ricotta, Gorgonzola, grated Parmigiano-Reggiano, and 2 tablespoons heavy cream in a medium-size heatproof bowl. Place bowl over simmering water, ensuring bottom of bowl does not touch water. Heat ricotta mixture, stirring often, until smooth, about 4 minutes. Remove from heat; set aside, and let thicken slightly, 2 to 4 minutes, stirring in up to remaining 1 tablespoon heavy cream, 1 teaspoon at a time, as needed to thin sauce.
Heat butter and thyme sprigs in a small skillet over medium. Cook, swirling skillet often, until butter is light golden brown and smells nutty, 2 to 3 minutes. Pour butter into a small heatproof bowl. Remove and discard thyme sprigs.
Transfer polenta to warmed serving bowls; top evenly with cheese sauce. Drizzle evenly with browned butter, and garnish with reserved toasted polenta. Serve immediately.