Preheat the oven to 350°F (175°C). Grease a 9×9-inch (or 8×8-inch) pan and line with parchment for easy removal.
Whisk the dry ingredients (flour, sugar, baking powder, salt) until evenly mixed.
In a separate bowl, whisk the wet ingredients (melted butter, milk, egg, vanilla, and almond extract if using) until smooth.
Pour the wet into the dry and stir just until combined; a few streaks are okay—overmixing can make the cake tougher.
Spread half of the batter into the prepared pan. Dollop cherry jam in small spoonfuls, then swirl gently with a knife. Top with the remaining batter and swirl again to create pockets of cherry speckle.
If using the crumb topping, mix the crumble ingredients with a fork until crumbly, then sprinkle over the batter in an even layer.
Bake for 40–45 minutes, until the edges are golden and a toothpick inserted into the center comes out with a few moist crumbs. The center should spring back lightly when touched.
Let the cake cool in the pan for about 15 minutes, then transfer to a rack. Dust with powdered sugar if you like and slice into squares for serving with coffee or tea.
