Preheat your oven to 350°F (175°C). If your brioche isn't day-old, dry the slices in a 300°F (150°C) oven for 8–10 minutes to firm them. Cut 8 thick slices (about 3/4" to 1" thick). Lightly spread about 1/4 tsp of softened unsalted butter on one side of each slice; set buttered side up on a parchment-lined baking sheet.

Make Almond Paste (Frangipane)

In a medium bowl, cream together 4 tbs softened unsalted butter and 1 tbs granulated sugar and 1 tbs light brown sugar until light and fluffy (about 1–2 minutes with a hand mixer).

Add 1 whole egg and mix until incorporated. Stir in 1 tsp almond extract and 1 tsp grated lemon zest.

Fold in 3 tbs almond flour and 1 tsp all-purpose flour until smooth and spreadable. The mixture should be a thick paste that holds its shape; if it's too loose chill 10 minutes.

Assemble and Bake

Using a spatula or the back of a spoon, spread about 1 to 1 1/2 tablespoons of the almond paste evenly over the buttered side of each brioche slice, leaving a small border (about 1/8" to 1/4").

Sprinkle each topped slice with about 1/2 tablespoon of sliced almonds, pressing lightly so they adhere.

Bake in the preheated 350°F (175°C) oven for 12–16 minutes, until the frangipane is set and lightly golden and the edges of the brioche are toasted. If you want a deeper color, briefly broil 30–60 seconds—watch closely to avoid burning.

Optional Soak & Finish

If using the optional soaking syrup, combine 1 tbs water and 1 tsp granulated sugar in a small saucepan; heat gently until sugar dissolves. Stir in 1 tsp liqueur or orange juice, remove from heat. Lightly brush about 1 teaspoon of the warm syrup onto each baked slice for extra moisture.

Let the bostocks cool on the baking sheet 5 minutes, then transfer to a rack. Dust lightly with powdered sugar and garnish with fresh berries or thin orange slices if desired. Serve warm or at room temperature.