Roast the walnuts in an oven preheated to 160℃. Finely chop the walnuts.
Put the frozen raspberries, sugar, and lemon juice in a small pot and simmer over medium heat for about 1 minute. Turn off the heat and add the cranberries and rum. Chill in the refrigerator.
[For the tart crust (pâte sucrée)]: Knead the butter and powdered sugar well. Then, add the egg, salt, and vanilla and beat until fluffy. Sift the dry ingredients into the dough.
Fold the dry ingredients into the dough, and just before the flouriness is gone, bring the dough together, wrap it in plastic wrap, and let it chill in the refrigerator for at least an hour.
[For the crumble]: In a bowl, mix together of all the ingredients except for the roasted walnuts and butter. Add the walnuts and butter and mix together until crumbly.
Chill the crumble and the almond cream in the refrigerator until you're ready to use them.
[For the almond cream (crème d'amande)]: Beat the butter and sugar well, then add the egg and beat some more. Add all of the remaining ingredients and mix well.
Preheat the oven to 180℃. Press the tart crust into the tart pan or ring. If using a tart pan, prick holes in the bottom of the crust with a fork.
Bake at 180℃ for 15 minutes. Once baked, quickly brush the entire surface of the crust with the beaten egg wash, then return the crust to the still-warm oven to dry in the residual heat.
Once the crust has completely cooled, pour in the mixture from Step 7. Scatter cranberries over the surface, leaving no gaps, then top with the crumble. Press down lightly with your hand.
Put the tart into an oven preheated to 180℃ and bake for 25 minutes. Dust with sugar using a tea strainer or similar to finish.
Story Behind this Recipe
I wanted to make a tart using vibrant cranberries and raspberries.
You can use sweetened framboise sauce (raspberry sauce) instead of frozen strawberries. In that case, omit the sugar and lemon juice and simply mix the cranberries with the sauce. One large sized egg is probably enough to take care of both the tart crust and the almond cream.