In a large bowl, combine lukewarm evaporated oat milk, instant yeast, and 1 teaspoon of sugar. Let sit for 5-10 minutes or until foamy.
Add the remaining sugar, flour, salt, butter, and vanilla. Knead for 8-10 minutes until smooth and soft. Scrape down the sides of the bowl as needed.
Cover and let the dough rise in a warm place for 60-90 minutes, until doubled in size.
Mix flour, sugar, and salt for the streusel. Rub in cold butter until chunky crumbs form. Don't overmix! Chill.
Turn dough onto a lightly floured surface and divide into 8-10 rolls. Shape into balls and place on a parchment-lined baking sheet and flatten slightly with your palm (no rolling pin needed).
Brush lightly with optional wash and generously cover the top of the dough with streusel.
Let rise for another 20-30 minutes.
Bake at 350°F (180°C / 160°C fan) for 18-22 minutes until lightly golden brown and baked through.
Cool slightly before serving.
Notes
Keep the rolls fairly pale for an authentic bakery look.
Chunky streusel is essential for these streusel rolls - so don’t overwork it.