For the toffee sauce: Melt the butter in a small saucepan over low heat, then add the sugar, molasses, espresso powder and salt. Whisk to work out any lumps, then continue to cook over low heat.
When bubbles appear at the edge of the pan, whisk in the cream and bring to a bare simmer. Remove the pan from the heat, cover and set aside.
For the cake: Position a rack in the center of the oven and heat to 350 degrees F.
Whisk together the flour, baking powder, baking soda and salt in a medium bowl and set aside.
Place 150 grams of the pitted dates and the boiling water in the bowl of a food processor fitted with the standard S-blade. Allow to soak for 2 minutes, then pulse 3 times.
Add the eggs, butter, both sugars, the vanilla extract and espresso powder to the food processor and pulse 5 times. Follow with the flour mixture and the remaining dates and pulse 3 more times.
Coat the bottom of each well in a 6-cup popover pan with 1 1/2 teaspoons of the toffee sauce. Follow with the batter, filling each cup 3/4 of the way full (see Cook's Note). You may have a few tablespoons of batter leftover depending on the size of your popover pan.
Bake for 11 minutes, then remove the pan from the oven and tap either on the oven door or countertop 3 times to deflate. Rotate the pan 180 degrees and bake another 11 minutes or until the middle of the cakes reach 210 degrees F.
Place the popover pan on a half-sheet pan and run a skewer around the outer rims to loosen the cakes. Pierce each cake several times with the skewer, poking all the way down to the bottom of the pan. Pour 1 tablespoon of toffee sauce over each pudding and let soak for 30 minutes.
When ready to serve, heat your broiler to high and broil the puddings until bubbly, 1 to 2 minutes. Remove and immediately run the skewer around the outer rims, cover with a clean sheet pan and invert to release.
Serve with more toffee sauce spooned over each pudding.
A number 10, 3.25-ounce disher works perfectly here if you have one.