Olive oil Yeast Pastry: Sprinkle yeast over 1/3 cup/75 mL lukewarm water; let stand until frothy, about 10 minutes.

In large bowl, whisk together all-purpose and whole wheat flours, sugar and salt. Make well in centre; pour in yeast mixture, oil and egg yolk and mix to thoroughly combine, adding 1/4 cup/60 mL to 1/2 cup/125 mL water, just until dough holds together. Transfer to lightly floured work surface; knead lightly until fairly smooth, about 2 minutes.

Cover and let stand at room temperature for 60 to 90 minutes or refrigerate overnight (let come to cool room temperature before rolling).

Reserving chard stems for another use, remove leaves; in large pot of boiling salted water, blanch until tender, 2 to 3 minutes. Drain, chill under cold water and drain well. Chop and set aside.

In skillet, heat oil over medium heat; add chorizo and fry until fat starts to render. Add onion and potato; increase heat to medium-high; fry, stirring often, until onion is softened and potato is tender, 12 to 15 minutes. Scrape into bowl; stir in eggs, then chard.

Divide dough into 2 pieces, one slightly larger. Roll larger piece into circle large enough to line 9-inch/23 cm greased pie plate; line plate, trimming to leave 1/2-inch/1 cm dough beyond rim.

Scrape chorizo mixture into pie shell. Roll out remaining dough into 10-inch/25 cm circle. Moisten rim of pie shell with water; top with dough circle, crimping together around rim. Cut centre hole in top; fit with pie bird or metal cylinder (such as piping tip) to prevent it closing. Bake in bottom third of 400F/200C oven until golden, 40 to 45 minutes. Let cool on rack before serving at room temperature.

Makes 8 to 10 servings.