Place the cream in a bowl and beat with an electric mixer until soft peaks form. Add the sugar and extract and beat until blended. Add the mascarpone and beat until stiff peaks form after just a minute or two. Refrigerate until needed. Preheat the grill to medium high heat. Brush the cut side of the peaches with the honey or maple syrup and grill cut side down for a couple of minutes until grill marks appear. Turn the peaches to create a cross-hatch pattern and grill another two minutes. Pipe the mascarpone cream into the center of each peach half, then sprinkle the nuts on top and serve immediately.