Heat oven to 300°. Place walnuts in the bowl of a food processor and pulse until ground, making sure not to overprocess into a paste. Add flour, ⅓ cup sugar, salt, and sage and pulse to incorporate. Add butter and pulse to form a coarse meal, about 30 seconds. Press dough into an ungreased 10-inch springform pan (or an 11x8-inch tart pan with removable bottom). Bake until light golden brown, about 55 minutes. Cool completely, then release from pan. In a small saucepan over medium-low heat, cook preserves until melted. Add cranberries, remaining ⅓ cup sugar, and cherry brandy. Bring to a simmer, stirring occasionally, and cook until cranberries have lost their shape, about 25 minutes. Remove from heat and let cool completely, about 1 hour. Spread Gorgonzola over tart crust in a thin, even layer. Top with a thin layer of the cooked cranberry mixture. Garnish with sage and walnut pieces. Divide into 10 even slices.