Blend together flour and sugar with an electric mixer. Add butter and blend until mixture resembles coarse meal (it will not form a dough). Transfer to a buttered 24cm springform pan and press evenly onto bottom. Bake in middle of oven until pale golden, about 30 minutes, then cool in pan on a rack.
Reduce temperature to 150 degrees C.
Make filling: Beat together crumbled Stilton, cream cheese and sugar in a large bowl with an electric mixer on low speed. Beat in flour and add eggs, 1 at a time, beating well after each addition. Beat in sour cream and vanilla then pour filling over cooled crust in pan.
Bake cheesecake in middle of oven until puffed and pale golden around edge, about 1 hour. Transfer cake in pan to a rack and run a knife around edge of pan to loosen. Cool completely, about 2 hours. Chill, covered, until cold, at least 4 hours. Remove side of pan and transfer cake to a plate.
Make compote while cake is cooling: Boil port, 1/2 cup sugar and peppercorns in a nonstick frypan, stirring until sugar is dissolved, until reduced to about 1/2 cup, 2 to 3 minutes. Add rhubarb and gently stir to coat. Simmer rhubarb, stirring gently once after 5 minutes until just tender but not falling apart, about 10 minutes, then transfer to a bowl. Chill compote covered until cold, at least 4 hours.
Make optional caramel topping: Just before serving, sprinkle 4 tablespoons sugar evenly over cheesecake and heat with a blowtorch, moving flame back and forth just over sugar until evenly melted and caramelised.
Cheesecake and compote can be chilled up to 2 days before caramelising top of cheesecake and serving.