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1
Preheat the oven to 400 degrees F.
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2
Make the crust: Pulse the oat flour, almond flour, tapioca flour, sugar, and salt together in a food processor for 5 seconds to blend.
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3
Add the cubed butter and pulse 8-10 times more until a moist, crumbly dough starts to form. Add the applesauce and blend until a soft dough forms.
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4
Divide the dough into 6 equal pieces and use your fingers to press the dough into 6 mini tart pans (or 1 9-inch tart pan if you don't have mini shells), making sure the dough rises slightly above the edges of each pan.
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5
Place the tarts on a rimmed baking sheet and freeze for 15 minutes while the oven heats.
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6
Bake the tarts for 10 minutes, until they start to brown at the edges. Remove from the oven and cool the crusts to room temperature.
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7
Reduce the oven heat to 375 degrees F.
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8
Make the filling: Beat the egg, almond paste, and applesauce together with an electric hand mixer on medium-low speed until smooth.
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9
Add the oat flour and powdered sugar, and beat on low speed to blend thoroughly.
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10
Divide the almond custard evenly between the cooled tart crusts.
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11
Pit and slice the peaches into 1/4-inch thick half-moons and fan the peach slices across each tart crust. Whisk the jam with 1 tablespoon water to make a glaze. Brush the peaches with the glaze using a pastry brush. Return the tarts to the oven and bake for 20-25 minutes more, until the custard is matte and puffy at the edges. Serve immediately.
