Preheat oven to 350°F (180°C). In a medium bowl, whisk together egg white, 1/3 cup (75 mL) sugar and 1/4 tsp (1 mL) salt until frothy. Add pecans and toss to coat. Spread evenly onto a parchment paper-lined baking sheet and toast in the oven, stirring a few times to break up nuts, for 15 min. or until lightly browned. Place pear slices on another baking sheet and dress with 1/2 tsp (2 mL) of olive oil and ground pepper. Roast in the oven, at the same time as the nuts, for 12 to 15 min. When cool enough to handle, separate nuts into pieces and cut 15 of the pear slices into 1/2-in. (1 cm) pieces. Set aside the remaining pear slice.
In a small blender, combine the remaining 1/3 cup (75 mL) of olive oil and mustard. Pour in cider vinegar with motor running until combined. Add the whole pear slice and remaining salt and sugar, and blend.
In a large bowl, toss the spinach and dressing. Adjust seasoning, if necessary. Add pear cubes and 1/3 cup (75 mL) candied pecans (save the rest for another use) and toss gently before serving.
A make-ahead wonder, the pecans can be prepared a week before. The dressing can be made three days ahead; store it in the fridge and whisk it before using.