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1
In large bowl, dissolve sugar in water.
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2
Sprinkle in yeast; let stand for 10 minutes or until frothy.
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3
Whisk in milk, eggs, egg yolks, oil and salt.
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4
With wooden spoon, stir in 3 cups (750 mL) of the flour to make soft dough.Turn out onto lightly floured surface; knead for 10 minutes, adding enough of the remaining flour to make dough smooth and elastic.
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5
Place in greased bowl, turning to grease all over.
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6
Cover with plastic wrap; let rise in warm draft-free place for 1 hour or until doubled in bulk.
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7
Filling: Meanwhile, in large skillet, heat butter with oil over high heat; cook onions, sugar and rosemary, stirring occasionally, for 5 minutes.
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8
Reduce heat to medium; cook, stirring and scraping up brown bits from bottom of pan, for 10 to 15 minutes or until onions are golden and very soft.
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9
Let cool to room temperature.
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10
Grease baking sheet or line with parchment paper; punch down dough.
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11
Turn out onto lightly floured surface.
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12
Roll out into 14- x 12-inch (35 x 30 cm) rectangle.
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13
Transfer to prepared pan.
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14
Spread mustard lengthwise in 3-inch (8 cm) strip down centre of rectangle, leaving 1-inch (2.5 cm) border uncovered at short ends; top with onion mixture.
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15
Sprinkle with 1 cup (250 mL) of the cheese.
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16
Using sharp knife and starting at 1 corner of dough, make diagonal cuts 1 inch (2.5 cm) apart almost to filling to form strips along 1 long side of dough.
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17
Repeat on other side, cutting diagonal strips in opposite direction.
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18
Alternating strips from each side, fold strips over filling to resemble braid, overlapping ends by 1 inch (2.5 cm) and brushing with some of the egg to seal.
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19
Cover with towel; let rise in warm place for 30 to 40 minutes or until doubled in bulk.
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20
Brush top with egg.
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21
Bake in centre of 350F (180C) oven for 30 to 40 minutes or until puffed and golden.
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22
Sprinkle remaining cheese down centre of braid; return to oven for 10 minutes or until melted.
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23
Serve warm or let cool completely on rack.
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24
(Make-ahead: Wrap in plastic wrap and refrigerate for up to 1 day; rewarm in oven before serving.
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25
).