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Preheat oven to 400 degrees.
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On a floured work surface, roll the dough out into a 12-inch round. Transfer to an ungreased baking sheet (though if you line it with parchment paper, it will be easier to transfer it to a plate later).
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Spread the ricotta mixture evenly over the bottom of the galette dough, leaving a 2-inch border. Shingle the zucchini attractively on top of the ricotta in concentric circles, starting at the outside edge.
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Drizzle the remaining tablespoon of the garlic and olive oil mixture evenly over the zucchini. Fold the border over the filling, pleating the edge to make it fit. The center will be open. Brush crust with egg yolk glaze.
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Bake the galette until the cheese is puffed, the zucchini is slightly wilted and the galette is golden brown, 30 to 40 minutes.
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Remove from the oven, sprinkle with basil, let stand for 5 minutes, then slide the galette onto a serving plate.
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Cut into wedges and serve hot, warm or at room temperature.