Portobello Mushroom Wellingtons

While mushroom caps bake, roughly chop mushroom stems. Peel, then mince or grate garlic. Strip 1/2 tbsp thyme leaves (dbl for 4 ppl) from stems. Roughly chop half the spinach. Heat a large non-stick pan over medium-high heat. When hot, add 1 tbsp butter (dbl for 4 ppl), then onions, mushroom stems, garlic and thyme. Cook, stirring often, until veggies soften, 3-4 min. Add chopped spinach. Stir until wilted, 1 min. Season with salt and pepper. 

Unroll puff pastry, discarding the wax paper, then place on a parchment-lined baking sheet. Cut pastry in half to create 2 rectangles. (NOTE: For 4 ppl, use 2 parchment-lined baking sheets and create 4 rectangles.) Arrange puff pastry rectangles at least 2 inches apart. Spoon spinach mixture onto one side of each pastry rectangle. Place mushroom caps on top of spinach filling, using 1 per pastry. Spread 1/2 tbsp mustard over each mushroom cap.

Working with one pastry rectangle at a time, fold the other side of pastry in half over filling. Using your fingers, firmly pinch the borders closed, then roll edges over to seal tightly. Bake Wellingtons in the middle of the oven until pastry is golden-brown and cooked through, 15-18 min. (NOTE: For 4 ppl, bake Wellingtons in the middle and top of the oven, switching positions halfway through.)

While Wellingtons bake, whisk together vinegar, remaining mustard, 1/2 tsp sugar and 2 tbsp oil (dbl for 4ppl) in a large bowl. Add cranberries, kale and remaining spinach. Season with salt and pepper, then toss to combine.