Brown the butter. Place the 100g salted butter in a light-colored saucepan over medium heat. Melt it fully, then continue cooking, swirling the pan frequently, until the butter foams, the foam subsides, and the milk solids at the bottom turn golden brown and smell nutty and toasty. Immediately pour into a large mixing bowl and allow to cool to room temperature.

Combine the flour, brown sugar, white sugar, and cinnamon in a bowl. Add the cold cubed butter and rub it in with your fingertips until the mixture resembles coarse, clumpy crumbles. Some larger pieces are fine, that is what creates the best texture. Refrigerate until needed.

To the cooled brown butter, add both sugars and whisk until well combined. Add the egg, egg yolk, and heavy cream and whisk again until the mixture is smooth and slightly glossy. Sift in the flour and baking powder and fold gently with a spatula until just combined and no dry streaks remain.

Cover the bowl and refrigerate the dough for 20 to 30 minutes until it is firm enough to handle and roll without sticking to your hands.

Weigh the dough and divide it into 8 equal balls of 67–69g each. Roll each one between your palms until smooth and place on a parchment-lined tray.

Press a generous amount of streusel firmly onto the top of each dough ball, ensuring good contact so it adheres properly. Place the tray in the freezer for 30 to 45 minutes.

About 15 minutes before the cookies come out of the freezer, place your baking sheet in the oven and preheat to 175°C (350°F), allowing the tray to heat up fully along with the oven.

Carefully transfer the frozen cookie balls directly onto the preheated baking sheet and bake for 12 to 13 minutes, until the edges are set and lightly golden and the streusel is toasted and fragrant. The centers will look soft — that is correct.

Leave the cookies on the hot tray for 5 to 8 minutes before transferring to a wire rack. This carry-over heat finishes setting the center without overbaking.

Mix equal parts powdered sugar and milk or heavy cream until you reach a thin, pourable consistency. Stir in a small amount of vanilla paste. Drizzle freely over the cooled cookies and allow the glaze to set for a few minutes before serving.