Kasutera Rusk (Crisp Castella Toasts)

Nov 7, 2026 · By VanillaGoods

Baking Cookies bars Easy

Kasutera rusk turns slices of honey-scented castella sponge into crisp, golden toasts with a buttery sugar crust. They shatter like biscotti but keep the caramel and honey flavor of the cake. Makes 20 pieces in about 1 hr 20 min.

Prep 15 min

Cook 45 min

Cooling 20 min

Total 1 hr 20 min

Yield 20 pieces

Ingredients

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pieces

10 ½ oz (300 g)castella (kasutera) cake, 1 loaf, day-old
3 tbsp (40 g)unsalted butter, melted
2 ½ tbsp (30 g)granulated sugar

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Instructions

Preheat the oven to 265°F (130°C) and set a wire rack on a baking sheet.
Trim the darker bottom paper layer off the castella (kasutera) cake if it is still attached. Cut the cake into 1/2-inch (12 mm) slices, then cut each slice in half to make about 20 pieces.
Arrange the pieces on the rack in a single layer and bake 15 minutes to dry the surfaces slightly.
Brush the tops of the pieces with the melted unsalted butter and sprinkle evenly with the granulated sugar.
Return to the oven and bake until the pieces are light golden, dry and crisp to the center when one is snapped, 25 to 30 minutes more.
Turn off the oven, prop the door open and leave the rusks inside 10 minutes, then cool completely on the rack, about 20 minutes; they crisp further as they cool.

Tips

Day-old castella slices more cleanly and dries faster than freshly baked cake.
Low heat is the key: higher temperatures brown the sugar before the centers dry out.
Any plain castella works, homemade or from a Japanese bakery.
Good with hot genmaicha or a cup of black coffee.

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Recipe FAQ

How long does it take to make kasutera rusk (crisp castella toasts)?

Plan on 15 minutes of prep and 45 minutes of cooking, plus 20 minutes to rest. The recipe makes 20 pieces.

How should I store kasutera rusk (crisp castella toasts)?

Store in an airtight container at room temperature up to 2 weeks.

Can I make kasutera rusk (crisp castella toasts) ahead?

It is at its best the day it is made; prepare it a few hours before serving.

Castella rusks are made in Japan by slicing the honey sponge cake known as kasutera, brushing it with butter and sugar and baking it slowly until crisp, a way to turn leftover cake into a long-keeping teatime treat. Serve it with hot genmaicha or a cup of black coffee.

Variations

Kokuto: replace the granulated sugar with 30 g (2 1/2 tbsp) finely ground kokuto (Okinawan black sugar); bake time unchanged.
Hojicha sugar: mix 3 g (1 1/2 tsp) hojicha (roasted green tea) powder into the sugar before sprinkling.
Honey butter: stir 15 g (2 tsp) honey into the melted butter and use only 15 g (1 tbsp) sugar; bake 5 minutes less and watch the color.

Estimated · per serving

Nutrition

Per serving = 1 of 20 servings this recipe makes.

77 Calories / serving

3.9g Fat

10.1g Carbs

0.6g Protein

6.8g Sugar

Whole recipe (20 servings): ~1540 cal · 78g fat · 202g carbs · 12g protein · 136g sugar

Estimated values per serving, calculated from standard ingredient data. Not verified Nutrition Facts; actual values vary with brands, measurements, and preparation.