Process the garlic to a paste in a food processor.

Continue to beat until mixture is light and fluffy, 8 to 10 minutes.With mixer running on medium speed, beat in strained jam and salt until just combined, about 1 minute.. Assemble the cake.

Place 1 cake layer on a cake plate.Using an offset spatula, spread 1 1/2 cups blueberry-coriander buttercream frosting from the center of the cake outward, forming a 1/2-inch-thick frosting layer with a 1-inch-wide, 3/4-inch-tall border around the perimeter to encase the curd.Spoon Meyer lemon curd in center of frosted layer; spread to edges of frosting border.

Top with remaining cake layer.Spread a thin layer of frosting over top and sides of cake.

Refrigerate 15 minutes.

Spread remaining frosting in a thick layer over top and sides of cake.Meanwhile, in a large skillet, melt the butter in the olive oil.

Add the leek and cook over low heat, stirring occasionally, until tender, about 5 minutes.Reserve 1/2 cup of the potato cooking water, then drain the peas and add them to the skillet.. Add the potatoes and the reserved cooking water to the skillet and bring to a simmer over moderate heat, stirring.

Add the mint, chives and lemon juice and season with salt and pepper.Remove the skillet from the heat and stir in the watercress.