To make the crust: Using a stand mixer, on low speed combine salt with flour. With mixer on low, add chopped butter gradually until mixture resembles coarse breadcrumbs. Add egg and water and mix on low to medium speed until dough comes together in a ball. Flatten ball of dough into a disk shape and wrap with film. Refrigerate until ready to use.

When rolling out dough, dust work surface with white rice flour. Sprinkle rice flour on disk of dough and roll out to fit a 9-inch pie pan. Place rolled dough in pan and press evenly on bottom and sides of pan. To partially prebake the pie shell, place a sheet of aluminum foil atop the pie shell. Add pie weights or dried beans to cover shell. Place pie pan on a cookie sheet and into preheated oven and bake 15-20 minutes until the edges are firm but not brown. Remove the baking sheet and piecrust from oven and remove the foil and pie weights. Let crust cool for a couple of minutes before returning the pan and crust to oven to bake an additional 2 minutes. Cool completely before filling.

To make the custard filling: Combine the sugar, flours, and salt in large bowl. Whisk in the melted butter followed by the honey until well combined. Add eggs and egg yolk one at a time and whisk well after each. Add heavy cream and lemon juice and combine. Whisk to combine. Strain the custard through a fine mesh sieve into the prepared pie shell. Bake in the middle of a 350° oven for 40-50 minutes. Rotate the pie after the edges have begun to set, about 35 minutes into the total baking time. The pie is finished baking when the edges are set and the center is no longer liquid but is still wobbly. Do not over bake. The custard will continue to cook after the pie is out of the oven. Cool on a wire rack 2-3 hours.

To make Rhubarb Sauce: Combine ingredients in small saucepan on the stove. Cook over a medium-low heat, stirring to combine. Cook 5-10 minutes until rhubarb softens. Remove from heat. Let cool and spoon contents into a glass jar. Store in refrigerator.