MAKE THE CHERRY JAM (CAN BE DONE 1-2 DAYS AHEAD):
Place halved, pitted cherries in a medium saucepan with the sugar and lemon juice. Set over low heat, stirring gently until the juices release and sugar dissolves completely.

Increase heat to medium and simmer, stirring frequently to prevent scorching, for about 20 minutes. The fruit should become very soft and the mixture noticeably thickened—it will continue to set as it cools.

Transfer jam to a heatproof bowl and allow to cool to room temperature. The jam can be refrigerated for up to 1 week.

PREPARE YOUR STEAMING SETUP:
Place an upturned small saucer or trivet in the bottom of a large, deep pot. Fill the pot about one-quarter full with hot water and bring to a gentle simmer over medium heat.

Generously grease the inside of your 1-quart (1-liter) pudding basin with softened butter, ensuring complete coverage up the sides.

Spoon 3 tablespoons of the cooled cherry jam into the bottom of the greased basin. Refrigerate briefly to firm up while you prepare the sponge.

If you don't have a snap-on lid, cut a 10-inch disc each of parchment paper and aluminum foil. Grease the parchment on one side. Create a 1-inch pleat across the center of each disc to allow for expansion during steaming.

MAKE THE ALMOND SPONGE:
In a large mixing bowl, beat the softened butter and light brown sugar with an electric hand mixer on medium-high speed for about 5 minutes. The mixture should become very pale, light, and fluffy—this step is critical for a light sponge.

With the mixer on medium speed, add the beaten eggs a little at a time, beating well after each addition. This prevents curdling. Add the almond extract with the final addition of egg.

Using a large metal spoon or spatula, gently fold in half of the sifted flour until just incorporated. Add 1 tablespoon of milk, then fold in the remaining flour. Add additional milk as needed—the batter should drop thickly from a spoon when tapped on the bowl's edge, forming a reluctant ribbon.

Gently fold in the almond flour until evenly distributed. Do not overmix—stop as soon as you no longer see streaks.

Carefully spoon the batter into the prepared pudding basin over the cherry jam. Spread the top level with a spatula, ensuring no air pockets remain.

STEAM THE PUDDING:
If using a snap-on lid, secure it firmly. If using parchment and foil, place the greased parchment (greased side down) over the basin, then the foil. Tie securely under the rim with kitchen string. Create a handle by looping additional string across the top and tying to the sides for easier lifting.

Carefully lower the basin onto the saucer in the simmering pot. The water should come about one-third up the sides of the basin. Cover the pot with a tight-fitting lid and maintain a gentle simmer.

Steam for 2 hours, checking every 30 minutes and topping up with boiling water as needed—never let it boil dry. Critical: Do not lift the pudding lid during steaming; this can cause the sponge to collapse.

MAKE THE VANILLA CUSTARD:
Pour the cream into a small heavy-bottomed saucepan. Scrape the vanilla seeds from the pod half and add both seeds and pod to the cream. Heat gently over low heat until steaming and just below a simmer—do not boil.

In a heatproof bowl, whisk together the egg yolks, cornstarch, and sugar until smooth, pale, and slightly thickened.

Remove vanilla pod from cream. Very slowly pour the hot cream into the egg mixture in a thin stream, whisking constantly to prevent scrambling.

Return the mixture to the saucepan and cook over low heat, stirring constantly with a wooden spoon or heatproof spatula. The custard is ready when it coats the back of the spoon and a line drawn through it holds—this takes 3-5 minutes. Do not boil or the eggs will curdle.

Pour custard through a fine-mesh sieve into a warmed serving jug. Keep warm by placing the jug in a bowl of hot water, or reheat gently before serving.

UNMOLD AND SERVE:
When the 2 hours are complete, carefully remove the basin from the pot. Remove the covering and let the pudding stand for 5 minutes—this allows it to set slightly and makes unmolding easier.

Run a thin palette knife or butter knife around the edge of the pudding to release it. Place a warm serving plate over the basin, then quickly and confidently invert. The pudding should release with a satisfying thunk and the cherry jam will cascade down the sides.

Arrange fresh raspberries around the base of the pudding and scatter toasted sliced almonds over the top. Serve generous wedges with warm vanilla custard.