Coarsely chop 1/4 cup almonds. Combine chopped almonds, brown sugar, and mustard in a bowl; mix well.
Cut Brie round horizontally in half. Place 1 half cut-side up in the center of a round baking stone. Spread half of the sugar mixture evenly over Brie. Top with the remaining half, cut-side up, and spread remaining sugar mixture on top. Sprinkle with remaining 1/4 cup sliced almonds.
Cut baguette diagonally in slices. Arrange slices around Brie and spray with cooking spray.
Bake in the preheated oven until baguette slices are golden brown and Brie begins to soften, 8 to 10 minutes. Remove from oven and let stand 5 minutes before serving.