Preheat oven to 350°F. Line a greased 8-inch square baking pan with parchment paper, leaving a 1- to 2-inch overhang.

Spread nuts evenly on a sheet pan and toast for 6-10 minutes, shaking the pan halfway through, until fragrant. Cool before roughly chopping.

In a small bowl, mix the rhubarb with the granulated sugar and set aside.

Brown the butter: Melt butter in a small saucepan over medium heat. Cook, stirring the pan every few seconds, until it turns a deep gold color and starts to smell fragrant, 3-5 minutes.

Pour the browned butter into a large mixing bowl. Add the light and dark brown sugars to the browned butter and whisk until smooth. Allow the butter mixture to cool (it should be warm, not hot).

Add the eggs and vanilla and fold until smooth.

Add the flour and salt and stir until the flour is almost completely incorporated.

Add the rhubarb-sugar mixture (leaving behind any sugary water) and the chopped nuts and chocolate. Mix until just combined.

Scrape the batter into prepared pan and smooth the surface.

Mix 1 ½ tablespoons granulated sugar with 1 ½ tablespoons turbinado sugar and sprinkle evenly over the top.

Bake for 25 to 30 minutes, until just set. Broil for an extra minute or two to caramelize the sugar, watching the oven closely so that the blondies don’t burn!

Remove the pan from the oven and cool completely on a wire rack.

Use the parchment overhang to lift the blondies out of the pan and onto a cutting board. Use a sharp knife to cut into 9 bars.

Store in an airtight container at room temperature for up to 4 days.