Would you believe this upside-down cake is gluten-free and low-calorie!?
Place nectarines in a heatproof bowl. Pour over the boiling water. Set aside for 1 hour to soak.
Preheat the oven to 180C/160C fan forced. Grease a round 21cm springform pan and line with baking paper.
Use electric beaters to beat butter in a large bowl until creamy. Add the honey and 1 teaspoon vanilla. Beat until pale. Add eggs, 1 at a time, beating well after each addition. Use a large metal spoon to gradually fold in the combined flours, baking powder and xanthan gum and the buttermilk, in alternating batches, until just smooth.
Drain nectarines, reserving liquid. Scatter half the pistachios over base of prepared pan. Add nectarines, cut side down. Sprinkle with remaining pistachios. Spoon over batter. Smooth surface. Bake for 50 minutes, until just firm to the touch or a skewer inserted into the centre comes out clean. Cool
Meanwhile, combine reserved liquid, extra honey and remaining vanilla in a saucepan over medium heat. Bring to the boil. Reduce heat and simmer for 8-10 minutes, until thickened slightly. Cool slightly.
Turn cake onto a plate. Pour over warm syrup. Serve with cream.
Instead of nectarine for the fruit layer, you could use dried apricot or peach halves.